1. In the name of God

3. Leukocyte abnormalities and interpretation of leukogram in animals

4. INTERPRETATION OF LEUKOCYTE RESPONSES The leukogram consists of the laboratory tests used in the routine evaluation of leukocyts on the CBC. The absolute concentration of each leukocyte type (not their percentage) is compared to appropriate reference intervals for that animal to detect any decrease or increase. In addition, microscopic changes in the morphology of leukocytes are noted on the stained blood smear, typically using the 100× oil-objective lens. The leukogram consists of the laboratory tests used in the routine evaluation of leukocyts on the CBC. The absolute concentration of each leukocyte type (not their percentage) is compared to appropriate reference intervals for that animal to detect any decrease or increase. In addition, microscopic changes in the morphology of leukocytes are noted on the stained blood smear, typically using the 100× oil-objective lens. If a significant number (>10%) of the leukocytes on the blood smear are smudged, pyknotic, or otherwise unidentifiable, the differential leukocyte count should be abandond. The counting of only recognizable leukocytes would produce percentages that are skewed because of the “ missing ” leukocyte types and inaccurate calculation of the absolute leukocyte concentrations. If a significant number (>10%) of the leukocytes on the blood smear are smudged, pyknotic, or otherwise unidentifiable, the differential leukocyte count should be abandond. The counting of only recognizable leukocytes would produce percentages that are skewed because of the “ missing ” leukocyte types and inaccurate calculation of the absolute leukocyte concentrations. Leukocytes, particularly neutrophils, begin to undergo apoptosis within hours after the blood sample is collected. In addition, exposure to the anticoagulant EDTA will induce cytoplasmic vacuolization and other morphologic changes in leukocytes. Refrigeration of the blood sample will not prevent these changes. If the blood sample will not be analyzed immediately or will be sent to an outside lab, a blood smear should be prepared, within minutes if possible. Leukocytes, particularly neutrophils, begin to undergo apoptosis within hours after the blood sample is collected. In addition, exposure to the anticoagulant EDTA will induce cytoplasmic vacuolization and other morphologic changes in leukocytes. Refrigeration of the blood sample will not prevent these changes. If the blood sample will not be analyzed immediately or will be sent to an outside lab, a blood smear should be prepared, within minutes if possible.

5. Whenever a blood smear is examined for the differential leukocytes count, any nRBCs encountered should be recorded as a separate tally. When the nRBCs exceeds 5 per 100 leukocytes, the initial “ leukocyte ” concentration must be adjusted: Whenever a blood smear is examined for the differential leukocytes count, any nRBCs encountered should be recorded as a separate tally. When the nRBCs exceeds 5 per 100 leukocytes, the initial “ leukocyte ” concentration must be adjusted: Corrected WBC conc. = (Initial WBC conc. × 100)/ (100 + # RBCs) Corrected WBC conc. = (Initial WBC conc. × 100)/ (100 + # RBCs) Conditions falsely increase the leukocyte concentration: a. Heinz bodies in erythrocytes (most common in cats) b. Clumped platelets or macroplatelets (most common in cats) c. Incomplete lysis of erythrocytes, especially reticulocytes form certain nondomestic animals (e.g., prairie dogs) d. Lipemia Conditions falsely decrease the total leukocyte concentration: a. Large platelet clumps that incorporate leukocytes and mask them b. Leukergy, when leukocytes occur in loose clusters or aggregates that are not counted as individual leukocytes. The error is corrected by collecting another blood sample that avoids the problem (platelet clumping or EDTA- induced leukergy).

6. Why is a fibrinogen test included on the CBC of some animals? Why is a fibrinogen test included on the CBC of some animals? Horses and ruminants often develop inflammatory disease without a significant change in the leukogram. However, inflammatory cytokines will induce hepatic hepatic production of several APPs including fibrinogen, which is included on large animal CBCs to augment the detection of inflammation. Although most often caused by inflammation, increased fibrinogen conc. Can also result from dehydration. Horses and ruminants often develop inflammatory disease without a significant change in the leukogram. However, inflammatory cytokines will induce hepatic hepatic production of several APPs including fibrinogen, which is included on large animal CBCs to augment the detection of inflammation. Although most often caused by inflammation, increased fibrinogen conc. Can also result from dehydration. Can leukocytosis interfere with tests on the CBC or chemistry pannel? Can leukocytosis interfere with tests on the CBC or chemistry pannel? The presence of marked leukocytosis (>50000 cells/μl) can affect the following tests: The presence of marked leukocytosis (>50000 cells/μl) can affect the following tests: Hb. The nuclei from ↑ WBC increase the turbidity of lysed blood, which can read as increased Hb. This artificially ↑ Hb leads to erroneous calculation of an ↑ MCHC. Hb. The nuclei from ↑ WBC increase the turbidity of lysed blood, which can read as increased Hb. This artificially ↑ Hb leads to erroneous calculation of an ↑ MCHC. When is a bone marrow evaluation indicated for evaluation of leukocytes? When is a bone marrow evaluation indicated for evaluation of leukocytes? When neutropenia is present, with ↓ granulopoiesis suspected as the cause, bone marrow evaluation should be considered. Marrow evaluation will document changes in M/E ratio, maturation sequences of neutrophilic precursors, morphologic abnormalities in neutrophilic precursors, and presence of abnormal cells in marrow. When neutropenia is present, with ↓ granulopoiesis suspected as the cause, bone marrow evaluation should be considered. Marrow evaluation will document changes in M/E ratio, maturation sequences of neutrophilic precursors, morphologic abnormalities in neutrophilic precursors, and presence of abnormal cells in marrow. What is the predominant blood leukocyte during health in the domestic animals? What is the predominant blood leukocyte during health in the domestic animals? In cats, dogs, and neonatal ruminants, neutrophils are the most abundant leukocyte, followed by lymphocytes. In mature ruminants, lymphocytes are the predominant leukocyte, with fewer neutrophils. In horses and pigs, numbers of neutrophils and lymphocytes are approximately equal. Eosinophils occur in very low numbers on blood smears from healthy animals, and basophils are almost never observed.

7. The blood concentration of various granulocytes (neutrophil, eosinophils, basophils) and monoeytes results from changes in the rate of release of these cells from the bone marrow into the blood, tbe distribution of these cells between circulating and marginal pools within the vasculature and the rate of emigration of cells from the blood into tissues. The blood concentration of various granulocytes (neutrophil, eosinophils, basophils) and monoeytes results from changes in the rate of release of these cells from the bone marrow into the blood, tbe distribution of these cells between circulating and marginal pools within the vasculature and the rate of emigration of cells from the blood into tissues. In essence, granulocytes and monocytes within the blood are in transit from the bone marrow to the tissues where they will perform their functions. In essence, granulocytes and monocytes within the blood are in transit from the bone marrow to the tissues where they will perform their functions. The concentration of lymphocytes in the blood, however, is primarily a reflection of changes in the kinetics of lymphocyte recirculation and cellular redistribution. The concentration of lymphocytes in the blood, however, is primarily a reflection of changes in the kinetics of lymphocyte recirculation and cellular redistribution.

8. Neutrophilia (Heterophilia)

9. Physiologic neutrophilia and heterophilia Physiologic neutrophilia and heterophilia Corticosteroid – induced neutrophilia and heterophilia Corticosteroid – induced neutrophilia and heterophilia neutrophilia and heterophilia of inflammation and infection neutrophilia and heterophilia of inflammation and infection

10. Physiologic neutrophilia and heterophilia

11. Leukogram findings Mild neutrophilia in mammals or heterophilia in birds is associated with up to a twofold increase of absolute cell counts in the absence of a left shift. Mild neutrophilia in mammals or heterophilia in birds is associated with up to a twofold increase of absolute cell counts in the absence of a left shift. Lymphocytosis is present and may be more dramatic than the neutrophilia in some species (e.g. cat, birds) Lymphocytosis is present and may be more dramatic than the neutrophilia in some species (e.g. cat, birds) Monocyte, eosinophil, and basophil counts remain within the reference interval. Monocyte, eosinophil, and basophil counts remain within the reference interval.

12. The duration of physiologic leukocytosis is approximately 20-30 minutes. The duration of physiologic leukocytosis is approximately 20-30 minutes.

13. Possible clinical findings at the lime of blood collection A young animal that is healthy but has experienced excitement or fear. A young animal that is healthy but has experienced excitement or fear. Evidence of increased heart rate, increased blood pressure, increased muscular activity, or seizures. Evidence of increased heart rate, increased blood pressure, increased muscular activity, or seizures.

14. Mechanism Epinephrine release in response to fear, excitement, or sudden exercise is responsible for physiologic neutrophilia and leukocytosis. Epinephrine release in response to fear, excitement, or sudden exercise is responsible for physiologic neutrophilia and leukocytosis. The neutrophilia is a pseudoneutrophilia. The neutrophilia is a pseudoneutrophilia. Increased heart rate, blood pressure, and blood flow causes mobilization of marginated neutrophils (MNP) with redistribution into the CNP. Increased heart rate, blood pressure, and blood flow causes mobilization of marginated neutrophils (MNP) with redistribution into the CNP.

15. Total blood neutrophil number (TBNP= CNP + MNP) is unchanged. Total blood neutrophil number (TBNP= CNP + MNP) is unchanged.

16. The concomitant lymphocytosis is explained by two theories : The concomitant lymphocytosis is explained by two theories : Epinephrine may block receptors on endothelial cells of postcapillary venules in lymph nodes, altering the normal recirculation pattern and preventing blood lymphocytes from reentering lymphoid tissue. Epinephrine may block receptors on endothelial cells of postcapillary venules in lymph nodes, altering the normal recirculation pattern and preventing blood lymphocytes from reentering lymphoid tissue. An unidentified source of lymphocytes, possibly from the thoracic duct, is released into the general circulation in response to epinephrine. An unidentified source of lymphocytes, possibly from the thoracic duct, is released into the general circulation in response to epinephrine.

17. Species characteristics Physiologic neutrophilia is uncommon in dogs Physiologic neutrophilia is uncommon in dogs Physiologic leukocytosis is common in young healthy cats, where the absolute neutrophil count may exceed 39,000/^1 and the absolute lymphocyte count may reach 36,000/^1. Neutrophilia is pronounced in the cat because of its larger MNP; however, the degree of lymphocytosis occasionally may exceed the magnitude of neutrophilia in some patients Physiologic leukocytosis is common in young healthy cats, where the absolute neutrophil count may exceed 39,000/^1 and the absolute lymphocyte count may reach 36,000/^1. Neutrophilia is pronounced in the cat because of its larger MNP; however, the degree of lymphocytosis occasionally may exceed the magnitude of neutrophilia in some patients

18. The response may occur in healthy cattle during parturition and strenuous exercise. WBC counts are 15,000-27,000/^1. Neutrophilia and lymphoeylosis occur but, unlike other species, eosinopenia is expected. The response may occur in healthy cattle during parturition and strenuous exercise. WBC counts are 15,000-27,000/^1. Neutrophilia and lymphoeylosis occur but, unlike other species, eosinopenia is expected. Physiologic leukocytosis also is common in young healthy horses. The total WBC count may reach 26,000//xl. The absolute neutrophil count may exceed 14,000//uJ, but the lymphocyte count seldom peaks above 14.400//xl. Physiologic leukocytosis also is common in young healthy horses. The total WBC count may reach 26,000//xl. The absolute neutrophil count may exceed 14,000//uJ, but the lymphocyte count seldom peaks above 14.400//xl.

19. Physiologic leukocytosis, especially lymphocytosis, accompanies lactation in sows, and it occurs in healthy pigs 3-5 hours after feeding. Physiologic leukocytosis, especially lymphocytosis, accompanies lactation in sows, and it occurs in healthy pigs 3-5 hours after feeding. Physiologic heterophilia is common in birds but relatively mild. Physiologic heterophilia is common in birds but relatively mild.

20. Corticosteroid – induced neutrophilia and heterophilia

21. Neulrophilia in mammals or heterophilia in birds, usually without a left shift. Neulrophilia in mammals or heterophilia in birds, usually without a left shift. Lymphopenia Lymphopenia Eosinopenia Eosinopenia Monocytosis in the dog and occasionally in the cat. Monocytosis in the dog and occasionally in the cat.

22. Possible clinical findings Conditions that cause endogenous corticosteroid release (e.g., pain, high and low body temperatures, captive environment of birds) Conditions that cause endogenous corticosteroid release (e.g., pain, high and low body temperatures, captive environment of birds)

23. Therapeutic use of corticosteroids The route of administration and dose affect the magnitude of the response. The route of administration and dose affect the magnitude of the response. The peak response occurs 4-8 hours after drug administration. The peak response occurs 4-8 hours after drug administration. The Icukogram usually returns to the reference interval within 24 hours after a single injection of short- acting glucocorticoid and within 2-3 days after cessation of long-term therapy (10 or more days). The Icukogram usually returns to the reference interval within 24 hours after a single injection of short- acting glucocorticoid and within 2-3 days after cessation of long-term therapy (10 or more days).

24. The neutrophil count will return to the reference interval after several weeks of continuous corticosteroid therapy, but lymphopenia usually persists. The neutrophil count will return to the reference interval after several weeks of continuous corticosteroid therapy, but lymphopenia usually persists. In hyperadrenocorticism, the magnitude of the neutrophilia diminishes with longevity of the disease, but other changes in the leokogram persist. In hyperadrenocorticism, the magnitude of the neutrophilia diminishes with longevity of the disease, but other changes in the leokogram persist.

25. Mechanisms Neutrophilia is due to an increase in the TBNP caused by multiple mechanisms : Neutrophilia is due to an increase in the TBNP caused by multiple mechanisms : Decreased emigration of neutrophils from circulation into the tissues and an increased blood transient time. Decreased emigration of neutrophils from circulation into the tissues and an increased blood transient time. Increased bone marrow release of neutrophils. The number of cells released is usually not sufficient to deplete the storage pool of segmenters to the extent that bands are released and a left shift occurs Increased bone marrow release of neutrophils. The number of cells released is usually not sufficient to deplete the storage pool of segmenters to the extent that bands are released and a left shift occurs

26. Decreased stickiness of neutrophils and a shift of cells from the MNP to the CNP. Decreased stickiness of neutrophils and a shift of cells from the MNP to the CNP. Similar mechanisms are assumed to exist in birds Similar mechanisms are assumed to exist in birds

27. Causes of lymphopenia Redistribution of recirculaling lymphocytes: they remain transiently sequestered in the lymphoid tissues or bone marrow rather than entering efferent lymph and blood. Redistribution of recirculaling lymphocytes: they remain transiently sequestered in the lymphoid tissues or bone marrow rather than entering efferent lymph and blood. Long-term usage of corticosteroids may cause lysis of thymic cortical lymphocytes and uncommitted lymphyocytes in the lymph nodes. Thymic medullary and bone marrow lymphocytes resist corticosteroid- induced lysis. Effector T- and B-cells do not lyse. Long-term usage of corticosteroids may cause lysis of thymic cortical lymphocytes and uncommitted lymphyocytes in the lymph nodes. Thymic medullary and bone marrow lymphocytes resist corticosteroid- induced lysis. Effector T- and B-cells do not lyse.

28. . Monocytosis may be caused by an effect similar to that on neutrophils (i.e.,. Monocytosis may be caused by an effect similar to that on neutrophils (i.e., mobilization of marginated cells within the blood vasculature) mobilization of marginated cells within the blood vasculature)

29. Causes of eosinopenia Margination or sequestration of eosinophils in the tissues. They resume circulation after cessation of the corticosteroid stimulation. Margination or sequestration of eosinophils in the tissues. They resume circulation after cessation of the corticosteroid stimulation. Inhibition of release of eosinophils from bone marrow. Eosinophilopoiesis continues and the total number of marrow eosinophils increases during corticosteroid stimulation. Inhibition of release of eosinophils from bone marrow. Eosinophilopoiesis continues and the total number of marrow eosinophils increases during corticosteroid stimulation.

30. Other possible mechanisms include inhibition of cytokines that govern eosinophil development and recruitment and induced apoptosis of eosinophils. Other possible mechanisms include inhibition of cytokines that govern eosinophil development and recruitment and induced apoptosis of eosinophils.

31. Species characteristics Dog

32. WBC counts are typically 15,000- 25,000//xl, but may reach 40,000/^1 on rare occasions. WBC counts are typically 15,000- 25,000//xl, but may reach 40,000/^1 on rare occasions. Neutrophilia without a left shift is typical, but immature neutrophils (up io 1,000/^1) may be released if the storage pool is depleted at the time of corticosteroid administration. Neutrophilia without a left shift is typical, but immature neutrophils (up io 1,000/^1) may be released if the storage pool is depleted at the time of corticosteroid administration. Lymphocyte counts commonly are decreased (less than 1,000//*1). Lymphocyte counts commonly are decreased (less than 1,000//*1). Monocytosis and eosinopenia are typically observed. Monocytosis and eosinopenia are typically observed.

33. Cat

34. The response is observed less frequently than in dogs. The response is observed less frequently than in dogs. The leukogram pattern is similar to that of dogs, but monocytosis is infrequent. The leukogram pattern is similar to that of dogs, but monocytosis is infrequent. The most extreme leukocytosis is about 30,000/^. The most extreme leukocytosis is about 30,000/^.

35. Cattle

36. In addition to general causes of the corticostcroid release (pain and temperature extremes), the response may occur with abomasal displacement, milk fever, ketosis. dystocia, feed overload, and indigestion. In addition to general causes of the corticostcroid release (pain and temperature extremes), the response may occur with abomasal displacement, milk fever, ketosis. dystocia, feed overload, and indigestion. WBC counts range from 8.000-18,000/^. WBC counts range from 8.000-18,000/^.

37. Eosinopenia caused by corticosteroids always occurs, but may be difficult to appreciate. Healthy cattle that are transported or placed in strange surroundings may have eosinopenia without other steroid- associated changes in the leukogram. Eosinopenia caused by corticosteroids always occurs, but may be difficult to appreciate. Healthy cattle that are transported or placed in strange surroundings may have eosinopenia without other steroid- associated changes in the leukogram.

38. Horse

39. This response may occur with sustained muscular exercise in healthy horses as well as with the usual causes of corticosleroid release. This response may occur with sustained muscular exercise in healthy horses as well as with the usual causes of corticosleroid release. WBC counts range up to 20,000/^.1 WBC counts range up to 20,000/^.1 Lymphopenia is seldom dramatic; lymphocyte counts are usually within the lower end of the reference interval (2,000//xl in young horses and l,500//xI in older horses). Lymphopenia is seldom dramatic; lymphocyte counts are usually within the lower end of the reference interval (2,000//xl in young horses and l,500//xI in older horses).

40. Birds

41. WBC counts may reach 35.000//xl. WBC counts may reach 35.000//xl. Moderate heterophilia may occur with counts ranging from 10,000- 25,000//xl. Moderate heterophilia may occur with counts ranging from 10,000- 25,000//xl. Lymphopenia (2,500-9,000/^ I) is most dramatic in avian species that have a predominance of lymphocytes in circulation in health. Lymphopenia (2,500-9,000/^ I) is most dramatic in avian species that have a predominance of lymphocytes in circulation in health.

42. neutrophilia and heterophilia of inflammation and infection

43. Leukogram changes Neutrophilia in mammals and heterophilia in birds. A left shift often is present. Neutrophilia in mammals and heterophilia in birds. A left shift often is present. A left shift is the classic response to inflammation, because the sudden demand for neutrophils or heterophils depletes the storage pool of segmenters and bands are released. A left shift is the classic response to inflammation, because the sudden demand for neutrophils or heterophils depletes the storage pool of segmenters and bands are released. There are exceptions to the generalization in: There are exceptions to the generalization in:

44. Mild inflammation may not be severe enough to cause a left shift; thus, a mature neutrophilia may exist. Mild inflammation may not be severe enough to cause a left shift; thus, a mature neutrophilia may exist. In long-standing inflammation, production of neutrophils may be balanced with tissue usage; a left shift does not occur. In long-standing inflammation, production of neutrophils may be balanced with tissue usage; a left shift does not occur. Not all inflammation elicits a purulent response. Therefore, neutrophilia would not occur. Not all inflammation elicits a purulent response. Therefore, neutrophilia would not occur.

45. During inflammation, endogenous release of cortisol in mammals or corticosterone in birds may secondarily cause neutrophilia or heterophilia, respectively, as described above. During inflammation, endogenous release of cortisol in mammals or corticosterone in birds may secondarily cause neutrophilia or heterophilia, respectively, as described above.

46. Lymphopenia and eosinopenia These are common findings in inflammation or infection. These are common findings in inflammation or infection. Endogenous release of cortisol in mammals or corticosterone in birds may contribute to these changes. Endogenous release of cortisol in mammals or corticosterone in birds may contribute to these changes. Because eosinophils are infrequent in the blood of cattle and birds (other than raptors), eosinopenia may be difficult to appreciate clinically in these species. Because eosinophils are infrequent in the blood of cattle and birds (other than raptors), eosinopenia may be difficult to appreciate clinically in these species.

47. Monocytosis This is an inconsistent finding in inflammation and infection. This is an inconsistent finding in inflammation and infection. Stress associated with inflammation may cause a steroid-induced monocytosis in the dog. Stress associated with inflammation may cause a steroid-induced monocytosis in the dog. Some forms of inflammation specifically elicit a monocytosis (e.g., granulomatous diseases, endocarditis). Some forms of inflammation specifically elicit a monocytosis (e.g., granulomatous diseases, endocarditis).

48. Clinical findings Obvious evidence of purulent or heterophilic inflammation may be evident. Obvious evidence of purulent or heterophilic inflammation may be evident. Purulent or heterophilic exudates may not be obvious with inflammation of the skin and mucosal surfaces because cells may be lost without much visible accumulation of matter. Purulent or heterophilic exudates may not be obvious with inflammation of the skin and mucosal surfaces because cells may be lost without much visible accumulation of matter. Certain types of inflammation lack significant neutrophilic or heterophilic exudation (e.g., hemorrhagic cystitis, seborrheic dermatitis, catarrhal enteritis, certain granulomatous reactions). Neutrophilia and heterophilia may or may not develop. Certain types of inflammation lack significant neutrophilic or heterophilic exudation (e.g., hemorrhagic cystitis, seborrheic dermatitis, catarrhal enteritis, certain granulomatous reactions). Neutrophilia and heterophilia may or may not develop.

49. Localized purulent diseases, such as pyometra or empyema, stimulate greater neutrophilic responses than generalized infections or septicemias. Birds do not form pus; however, heterophil degranulation may provoke granuloma formation. Localized purulent diseases, such as pyometra or empyema, stimulate greater neutrophilic responses than generalized infections or septicemias. Birds do not form pus; however, heterophil degranulation may provoke granuloma formation. If a localized site of purulent or heterophilic inflammation is surgically extirpated, an exacerbation of neutrophilia or heterophilia should be anticipated during the immediate postsurgical period. If a localized site of purulent or heterophilic inflammation is surgically extirpated, an exacerbation of neutrophilia or heterophilia should be anticipated during the immediate postsurgical period.

50. Mechanisms Infectious agents and products of tissue injury stimulate a variety of cells to release interleukins, growth factors, cytokines, and other mediators of inflammation that are interrelated in causing neutrophil or heterophil proliferation, maturation, and release from the bone marrow into blood. These cells subsequently emigrate from the blood into tissues. The result of these activities on the numbers of blood neutrophils in mammals, or heterophils in birds, may be immediate or delayed for several days. Infectious agents and products of tissue injury stimulate a variety of cells to release interleukins, growth factors, cytokines, and other mediators of inflammation that are interrelated in causing neutrophil or heterophil proliferation, maturation, and release from the bone marrow into blood. These cells subsequently emigrate from the blood into tissues. The result of these activities on the numbers of blood neutrophils in mammals, or heterophils in birds, may be immediate or delayed for several days.

51. In mammals, an early, transient, endo toxin-mediated effect causes increased adhesiveness of neutrophils, retention of neutrophils in the MNP, and subsequent emigration into the tissues. This effect may result in a short-term neutropenia. Neutrophilia quickly follows because of an increased release of neutrophils from the bone marrow storage pool into the blood. Some birds appear to be refractory to the effects of endotoxin. In mammals, an early, transient, endo toxin-mediated effect causes increased adhesiveness of neutrophils, retention of neutrophils in the MNP, and subsequent emigration into the tissues. This effect may result in a short-term neutropenia. Neutrophilia quickly follows because of an increased release of neutrophils from the bone marrow storage pool into the blood. Some birds appear to be refractory to the effects of endotoxin.

52. Following infection, inflammation, or endotoxin effects, cells in the neutrophil lineage are stimulated to proliferate and differentiate. These cells include the following: Following infection, inflammation, or endotoxin effects, cells in the neutrophil lineage are stimulated to proliferate and differentiate. These cells include the following:

53. Multipotential stem cells Multipotential stem cells Neutropbil progenitor cells (CFU-GM, CFU-G) Neutropbil progenitor cells (CFU-GM, CFU-G) Mitotic precursors in the bone marrow proliferativc cell pool (myeloblasts, promyelocytes, and neutrophilic myelocytes) Mitotic precursors in the bone marrow proliferativc cell pool (myeloblasts, promyelocytes, and neutrophilic myelocytes)

54. The number of neutrophils in blood during purulent inflammation reflects a balance between the rate of release of cells from the bone marrow, the rate of emigration of cells from blood into tissues, and the rate of cell utilization within tissues (tissue demand). The number of neutrophils in blood during purulent inflammation reflects a balance between the rate of release of cells from the bone marrow, the rate of emigration of cells from blood into tissues, and the rate of cell utilization within tissues (tissue demand). If bone marrow release is greater than cellular emigration into the tissues, neutrophilic leukocytosis occurs. If bone marrow release is greater than cellular emigration into the tissues, neutrophilic leukocytosis occurs.

55. If the emigration of cells from the vasculature exceeds the rate of replacement by the bone marrow (occurs with excessive tissue demand for neutrophils). neutropenia occurs. If the emigration of cells from the vasculature exceeds the rate of replacement by the bone marrow (occurs with excessive tissue demand for neutrophils). neutropenia occurs. During purulent inflammation, a variable WBC count (from very low to very high) is possible depending on this balance. During purulent inflammation, a variable WBC count (from very low to very high) is possible depending on this balance. A similar process explains the degree of heterophilia in avian patients. A similar process explains the degree of heterophilia in avian patients.

56. With an increased tissue demand for neutrophils and an increase in the bone marrow release rate of these cells, the marrow storage pool may become depleted of segmenters. Band neutrophils and younger forms (neutrophilic metamyelocytes and myelocytes) may appear in blood following severe tissue demands for neutrophils. With an increased tissue demand for neutrophils and an increase in the bone marrow release rate of these cells, the marrow storage pool may become depleted of segmenters. Band neutrophils and younger forms (neutrophilic metamyelocytes and myelocytes) may appear in blood following severe tissue demands for neutrophils. When the total neutrophil count is within the reference interval or neutrophilia is present, a clinically important left shift exists when any of the following is present: When the total neutrophil count is within the reference interval or neutrophilia is present, a clinically important left shift exists when any of the following is present:

57. Bands and other immature neutrophils are >l,O0G//xl in dogs and cats. Bands and other immature neutrophils are >l,O0G//xl in dogs and cats. Bands and other immature neutrophils are >300//t in large animals. Bands and other immature neutrophils are >300//t in large animals. In birds, a clinically important left shift is present when heterophilic bands are >1,000//il. Left shifts are more difficult to identify in stained avian blood smears because heterophils have less nuclear lobulation and the prominent cytoplasmic granules may obscure nuclear morpohology. In birds, a clinically important left shift is present when heterophilic bands are >1,000//il. Left shifts are more difficult to identify in stained avian blood smears because heterophils have less nuclear lobulation and the prominent cytoplasmic granules may obscure nuclear morpohology.

58. A left shift is the hallmark of infection or severe inflammation: however, left shifts can occur in noninflammatory diseases (e.g.. immune-mediated hemolytic anemia). A left shift is the hallmark of infection or severe inflammation: however, left shifts can occur in noninflammatory diseases (e.g.. immune-mediated hemolytic anemia). When neutropenia in mammals or heteropenia in birds is present and more than 10% of the total blood neutrophil number are immature cells, high tissue demand for neutrophils exists. When neutropenia in mammals or heteropenia in birds is present and more than 10% of the total blood neutrophil number are immature cells, high tissue demand for neutrophils exists.

59. The magnitude of the left shift lends to parallel the intensity of the purulent or heterophilic inflammation. The magnitude of the left shift lends to parallel the intensity of the purulent or heterophilic inflammation. In certain severe purulent diseases, marked neutrophilia may be accompanied by a left shift that includes myelocytes, progranulocytes, or myeloblasts in blood. This is called a "leukemoid response" because of its similarity to the blood profile of acute granulocytic leukemia. In certain severe purulent diseases, marked neutrophilia may be accompanied by a left shift that includes myelocytes, progranulocytes, or myeloblasts in blood. This is called a "leukemoid response" because of its similarity to the blood profile of acute granulocytic leukemia.

60. During chronic, established, suppurative diseases, the rate of neutrophil production in the bone marrow eventually exceeds the rate of neutrophil release from the bone marrow and the rate of tissue utilization of neutrophils. As the marrow storage pool is replenished, the left shift diminishes or disappears despite a continued tissue demand for neutrophils. During chronic, established, suppurative diseases, the rate of neutrophil production in the bone marrow eventually exceeds the rate of neutrophil release from the bone marrow and the rate of tissue utilization of neutrophils. As the marrow storage pool is replenished, the left shift diminishes or disappears despite a continued tissue demand for neutrophils. This mature neutrophilia persists until cell demand and production are balanced; the neutrophil count subsequently reiurns to the reference interval. This mature neutrophilia persists until cell demand and production are balanced; the neutrophil count subsequently reiurns to the reference interval.

61. Species characteristics Species characteristics

62. Dog

63. WBC counts between 10,000 and 30,000//xJ are common. A few cases will have counts that exceed 50,000/juJi and in rare cases counts may exceed 100,000/^1. WBC counts between 10,000 and 30,000//xJ are common. A few cases will have counts that exceed 50,000/juJi and in rare cases counts may exceed 100,000/^1. In contrast, neutropenia may result from overwhelming Gram-negative sepsis (e.g., salmonellosis, parvoviral enteritis) of the lung, thorax, peritoneum, intestine, or uterus. Endotoxemia may be a contributory factor. In contrast, neutropenia may result from overwhelming Gram-negative sepsis (e.g., salmonellosis, parvoviral enteritis) of the lung, thorax, peritoneum, intestine, or uterus. Endotoxemia may be a contributory factor.

64. Leukcmoid reactions and extreme neutrophilia may be associated with WBC counts exceeding 100,000/jW.l. Examples include localized infection (e.g., pyometra), certain forms of parasitism (e.g., hepatozoonosis), and genetic disorder (e.g., canine leukocyte adhesion deficiency). Leukcmoid reactions and extreme neutrophilia may be associated with WBC counts exceeding 100,000/jW.l. Examples include localized infection (e.g., pyometra), certain forms of parasitism (e.g., hepatozoonosis), and genetic disorder (e.g., canine leukocyte adhesion deficiency).

65. Cat

66. WBC counts between 10.000 and 30,000/jiaI are common. A few cases have counts that exceed 30,000//xl, and in rare cases counts may exceed 75,000/^1. WBC counts between 10.000 and 30,000/jiaI are common. A few cases have counts that exceed 30,000//xl, and in rare cases counts may exceed 75,000/^1. Gram-negative sepsis and endotoxemia cause neutropenia in cats as described for dogs. Gram-negative sepsis and endotoxemia cause neutropenia in cats as described for dogs.

67. Cattle

68. Inflammatory leukograms in calves up to 3 or 4 months old may be similar to those described for cats and dogs, except that left shifts may be more subtle. Inflammatory leukograms in calves up to 3 or 4 months old may be similar to those described for cats and dogs, except that left shifts may be more subtle. Fibrinous, nonpurulent inflammation in cattle (e.g.. early stages of shipping fever pneumonia) elicit little or no neutrophil response. Hyperfibrinogenemia (high plasma fibrinogen concentration) may be the first or only laboratory sign of inflammatory disease. Fibrinous, nonpurulent inflammation in cattle (e.g.. early stages of shipping fever pneumonia) elicit little or no neutrophil response. Hyperfibrinogenemia (high plasma fibrinogen concentration) may be the first or only laboratory sign of inflammatory disease.

69. In adult cattle, acute purulent inflammation frequently causes leukopenia, neutropenia, severe left shift, and lymphopenia. This leukogram pattern lasts 24^18 hours. If the animal survives, neutrophil counts return toward the reference interval with a persisting left shift In adult cattle, acute purulent inflammation frequently causes leukopenia, neutropenia, severe left shift, and lymphopenia. This leukogram pattern lasts 24^18 hours. If the animal survives, neutrophil counts return toward the reference interval with a persisting left shift

70. Persistent purulent inflammation is associated with WBC counts ranging from 4.000-15,000//^1, with a predominance of neutrophils. This change is often called a "neutrophil- lymphocyte reversal" because lymphocytes predominate in the blood of healthy cattle. Lymphocyte numbers are reduced by endogenous corticosteroid release during inflammatory disease. Persistent purulent inflammation is associated with WBC counts ranging from 4.000-15,000//^1, with a predominance of neutrophils. This change is often called a "neutrophil- lymphocyte reversal" because lymphocytes predominate in the blood of healthy cattle. Lymphocyte numbers are reduced by endogenous corticosteroid release during inflammatory disease.

71. Infrequently, bovine patients have neulrophil counts that exceed 30.000/ fi\. In rare cases (e.g., empyema), counts may exceed 60.000/^,1. Counts exceeding 100,000/^1 may be observed in Holstein cattle with leukocyte adhesion deficiency. Because of the lack of proper adhesion molecule expression, neutrophils fail to emigrate from the vasculature and migrate to sites of tissue injury or infection. Infrequently, bovine patients have neulrophil counts that exceed 30.000/ fi\. In rare cases (e.g., empyema), counts may exceed 60.000/^,1. Counts exceeding 100,000/^1 may be observed in Holstein cattle with leukocyte adhesion deficiency. Because of the lack of proper adhesion molecule expression, neutrophils fail to emigrate from the vasculature and migrate to sites of tissue injury or infection.

72. Horse

73. WBC counts are typically 7,000-20,000/^1. Rarely, the leukocyte count may exceed 30,000/^,1. WBC counts are typically 7,000-20,000/^1. Rarely, the leukocyte count may exceed 30,000/^,1. Left shifts associated with neutrophilia are generally moderate in the horse. Infrequently, diseases of the gastrointestinal tract associated with endotoxemia (e.g., acute salmonellosis) will be characterized by a severe left shift with leukopenia or a total WBC count within the reference interval Left shifts associated with neutrophilia are generally moderate in the horse. Infrequently, diseases of the gastrointestinal tract associated with endotoxemia (e.g., acute salmonellosis) will be characterized by a severe left shift with leukopenia or a total WBC count within the reference interval

74. Because neutrophil response to inflammation is frequently mild, hyperfibrinogenemia has been used as another indicator of inflammation. Because neutrophil response to inflammation is frequently mild, hyperfibrinogenemia has been used as another indicator of inflammation.

75. Birds

76. WBC counts are typically 24,000-45,000/^1. Occasionally, WBC counts may exceed 100,000-125,000//i] with salmonellosis, mycobacteriosis, or aspergillosis. WBC counts are typically 24,000-45,000/^1. Occasionally, WBC counts may exceed 100,000-125,000//i] with salmonellosis, mycobacteriosis, or aspergillosis. Left shifts are more difficult to discern because avian heterophils have fewer nuclear lobes than mammalian neutrophils in health. Cytoplasmic granules also may obscure nuclear morphology Left shifts are more difficult to discern because avian heterophils have fewer nuclear lobes than mammalian neutrophils in health. Cytoplasmic granules also may obscure nuclear morphology

77. “ Heterophil-lymphocyte reversal ” may be observed in avian species with a predominance of circulating lymphocytes (as is the case in adult cattle). “ Heterophil-lymphocyte reversal ” may be observed in avian species with a predominance of circulating lymphocytes (as is the case in adult cattle).

78. Other cause of neutrophilia Tissue necrosis and ischemia Tissue necrosis and ischemia Immune-mediated diseases with cell and tissue damage Immune-mediated diseases with cell and tissue damage Toxemia/toxicosis Toxemia/toxicosis Hemorrhage Hemorrhage Hemolysis Hemolysis Neoplasia. including nonspecific malignancies and myeloproliferative disorders involving neutrophils Neoplasia. including nonspecific malignancies and myeloproliferative disorders involving neutrophils

79. Neutropenia and heteropenia

80. A) Margination of circulating neutrophils (pseudoneutropenia). A) Margination of circulating neutrophils (pseudoneutropenia). Neutrophils shift from the CNP to MNP as blood flow slows or as adhesion molecules are expressed on die cell membranes of neutrophils and endothelial cells. Neutrophils shift from the CNP to MNP as blood flow slows or as adhesion molecules are expressed on die cell membranes of neutrophils and endothelial cells. Endotoxin initially stimulates only margination of neutrophils (pseudoneutropenia); however, increased emigration of neutrophils from blood ultimately results in transition to a true neutropenia. Endotoxin initially stimulates only margination of neutrophils (pseudoneutropenia); however, increased emigration of neutrophils from blood ultimately results in transition to a true neutropenia.

81. Birds may be refractory to these effects of endotoxin. Birds may be refractory to these effects of endotoxin.

82. B) Excessive tissue demand for or destruction of neutrophils in mammals and heterophils in birds. B) Excessive tissue demand for or destruction of neutrophils in mammals and heterophils in birds. Neutnipenia occurs in inflammation or infection when the rate of emigration of neutrophils from the vasculature into the tissues exceeds the rate of replacement of these cells in the blood by the bone marrow : Neutnipenia occurs in inflammation or infection when the rate of emigration of neutrophils from the vasculature into the tissues exceeds the rate of replacement of these cells in the blood by the bone marrow :

83. Left shifts are common Left shifts are common Toxic change is likely, considering the causes of disease Toxic change is likely, considering the causes of disease Neutropenia occurs commonly in cattle, but does not carry as grave a prognosis as in other species. Neutropenia occurs commonly in cattle, but does not carry as grave a prognosis as in other species. Neutropenia is found in peracute or acute inflammation before granulopoietic hyperplasia has time to occur in the bone marrow. Neutropenia is found in peracute or acute inflammation before granulopoietic hyperplasia has time to occur in the bone marrow.

84. Granulocytic hyperplasia in bone marrow usually follows with time and can have an effect on the WBC count within 48- 72 hours. Granulocytic hyperplasia in bone marrow usually follows with time and can have an effect on the WBC count within 48- 72 hours. Similar changes occur with avian heterophils. Similar changes occur with avian heterophils.

85. Immune-mediated destruction of circulating neulrophils with concurrent neutropenia is rare in animals. Neutropenia has been observed rarely with hemolytic disease of newborn foals and with drug administration. This mechanism has not been reported in birds. C. Reduced production of neutrophils in mammals and heterophils in birds: Immune-mediated destruction of circulating neulrophils with concurrent neutropenia is rare in animals. Neutropenia has been observed rarely with hemolytic disease of newborn foals and with drug administration. This mechanism has not been reported in birds. C. Reduced production of neutrophils in mammals and heterophils in birds:

86. Radiation, cytotoxic drugs used in cancer chemotherapy or immunosuppressive therapy, and some other drugs predictably cause neutropenia: Radiation, cytotoxic drugs used in cancer chemotherapy or immunosuppressive therapy, and some other drugs predictably cause neutropenia:

87. Thrombocytopenia and anemia (pancytopenia or aplastic anemia) may follow. Thrombocytopenia and anemia (pancytopenia or aplastic anemia) may follow. Infections are considered imminent when neutrophil counts are 500//xJ or lower. Infections are considered imminent when neutrophil counts are 500//xJ or lower. Cytotoxic drugs also cause predictable heteropenia in birds. Cytotoxic drugs also cause predictable heteropenia in birds. Idiosyncratic drug reactions can cause neutropenia in mammals and heteropenia in birds. Idiosyncratic drug reactions can cause neutropenia in mammals and heteropenia in birds.

88. Neutropenia is a common feature of diseases affecting hematopoietic stem cells (e.g. pancytopenia or aplastic anemia) Neutropenia is a common feature of diseases affecting hematopoietic stem cells (e.g. pancytopenia or aplastic anemia)

89. Certain viral and rickettsia infections : Certain viral and rickettsia infections : In mammals, a characteristic period of neutropenia may be present due to the death of progenitor cells and proliferating granulocytes in the bone marrow (e.g., feline infectious panleukopenia, canine parvoviral enteritis, feline leukemia virus (FeLV) and feline immunodeficiency virus (FiV) infections, ehrlichiosis). Endotoxemia secondary to enteric lesions also may play an important role in some viral infections, In birds, heteropenia may be associated with circovirus, herpesvirus, polyomavirus, and reovirus infections. In mammals, a characteristic period of neutropenia may be present due to the death of progenitor cells and proliferating granulocytes in the bone marrow (e.g., feline infectious panleukopenia, canine parvoviral enteritis, feline leukemia virus (FeLV) and feline immunodeficiency virus (FiV) infections, ehrlichiosis). Endotoxemia secondary to enteric lesions also may play an important role in some viral infections, In birds, heteropenia may be associated with circovirus, herpesvirus, polyomavirus, and reovirus infections.

90. Diminished bone marrow production of granulocytes may be a transient feature during preclinical and acute stages of many viral diseases. Granulopoietic hyperplasia, reflecting recovery, may be encountered in bone marrow aspirates by the time neutropenia is observed. Diminished bone marrow production of granulocytes may be a transient feature during preclinical and acute stages of many viral diseases. Granulopoietic hyperplasia, reflecting recovery, may be encountered in bone marrow aspirates by the time neutropenia is observed.

91. Cyclic hematopoiesis (neutropenia) has been reported in animals: Cyclic hematopoiesis (neutropenia) has been reported in animals:

92. Cyclic hematopoiesis of gray collie dogs has an autosomal recessive pattern of inheritance. Cyclic hematopoiesis of gray collie dogs has an autosomal recessive pattern of inheritance. Periods of neutropenia occur at 11-14 day intervals. Periods of neutropenia occur at 11-14 day intervals. The disease is presumed to result from a defect in stem cell regulation. The disease is presumed to result from a defect in stem cell regulation. Cyclic activity also affects erythrocytes and platelets. Cyclic activity also affects erythrocytes and platelets. Cyclic hematopoiesis occurs rarely in FeLV-infected cats Cyclic hematopoiesis occurs rarely in FeLV-infected cats

93. Cyclophosphamide therapy may induce cyclic hematopoiesis in dogs. Cyclophosphamide therapy may induce cyclic hematopoiesis in dogs.

94. Neutropenia may be a manifestation of idiosyncratic drug reaction (e.g., chloramphenicol in cats, phenylbutazone. cephalosporin antibiotics, griscofulvin, and estrogen toxicosis in dogs). Neutropenia may be a manifestation of idiosyncratic drug reaction (e.g., chloramphenicol in cats, phenylbutazone. cephalosporin antibiotics, griscofulvin, and estrogen toxicosis in dogs). Inherited familial neutropenia has been observed in Standardbred horses and Belgian Tervuren dogs. The horses had signs of illness, suggesting that the neutropenia was pathologic. The dogs were clinically healthy, suggesting that their neutropenia was benign, as has been observed in some humans. Inherited familial neutropenia has been observed in Standardbred horses and Belgian Tervuren dogs. The horses had signs of illness, suggesting that the neutropenia was pathologic. The dogs were clinically healthy, suggesting that their neutropenia was benign, as has been observed in some humans.

95. Excessive ineffective granulopoesis : Excessive ineffective granulopoesis :

96. This condition is uncommon except in cats with FeLV infection and myelodysplastic syndrome. This condition is uncommon except in cats with FeLV infection and myelodysplastic syndrome. Bone marrow examination reveals granulocytic hyperplasia concomitant with neutropenia. Bone marrow examination reveals granulocytic hyperplasia concomitant with neutropenia. The bone marrow proliferating pool is expanded with a concomitant decrease in the maturation and storage pool of neutrophils, giving the appearance of a shift toward immaturity. A predominance of promyelocytes suggests a "maturation arrest" of neutrophil development. The bone marrow proliferating pool is expanded with a concomitant decrease in the maturation and storage pool of neutrophils, giving the appearance of a shift toward immaturity. A predominance of promyelocytes suggests a "maturation arrest" of neutrophil development.

105. Monocytosis

106. Monocytosis can occur any time that neutrophilia occurs, because both cell lines are derived from a common bipotential stem cell. Monocytosis can occur any time that neutrophilia occurs, because both cell lines are derived from a common bipotential stem cell. Monocytosis is the least characteristic change in the leukogram in response to corticosteroids, except in the dog. Monocytosis is the least characteristic change in the leukogram in response to corticosteroids, except in the dog. Monocytosis may be observed in both acute and chronic stages of disease. Monocytosis may be observed in both acute and chronic stages of disease. Monocytosis heralds the recovery from neutropenia. Because there is no bone marrow storage pool for monocytes, these cells arc released into the blood at an earlier age than neutrophils. Monocytosis heralds the recovery from neutropenia. Because there is no bone marrow storage pool for monocytes, these cells arc released into the blood at an earlier age than neutrophils.

107. Monocytosis may be the most prominent change in the leukogram during bacterial endocarditis and bacteremia. Monocytosis may be the most prominent change in the leukogram during bacterial endocarditis and bacteremia. Disorders characterized by suppuration, necrosis, malignancy, hemolysis,hemorrhage, immune-media ted injury, and certain pyogranulomatous diseases may be associated with, monocytosis. Marked monocytosis also may be observed in birds with chlamydophilosis (chlamydiosis, omilhosis, psittacosis). This disease is caused by Chlamydophila psittaci(formerly known as Chlamydiu psittaci), an obligate, intracellular, Gram-negative bacterium that lacks a cell wall. Disorders characterized by suppuration, necrosis, malignancy, hemolysis,hemorrhage, immune-media ted injury, and certain pyogranulomatous diseases may be associated with, monocytosis. Marked monocytosis also may be observed in birds with chlamydophilosis (chlamydiosis, omilhosis, psittacosis). This disease is caused by Chlamydophila psittaci(formerly known as Chlamydiu psittaci), an obligate, intracellular, Gram-negative bacterium that lacks a cell wall.

108. Monocytopenia

109. This linding is not a clinically useful feature of leukograms This linding is not a clinically useful feature of leukograms

110. Eosinophilia

111. Eosinophilia generally is associated with parasitic infection or hypersensitivity. Eosinophilia generally is associated with parasitic infection or hypersensitivity. Animals with eosinophilic disorders may have a response tempered by a concomitant corticosteroid effect (an eosinopenic effect). Animals with eosinophilic disorders may have a response tempered by a concomitant corticosteroid effect (an eosinopenic effect). Frequently, localized lesions that contain significant numbers of eosinophils in the exudate are not accompanied by eosinophilia in the blood (e.g., eosinophilic granuloma). Frequently, localized lesions that contain significant numbers of eosinophils in the exudate are not accompanied by eosinophilia in the blood (e.g., eosinophilic granuloma).

112. The tissues most commonly affected in eosinophilic hypersensitivity conditions are rich in mast cells and include skin, lung, gastrointestinal tract, and uterus. The tissues most commonly affected in eosinophilic hypersensitivity conditions are rich in mast cells and include skin, lung, gastrointestinal tract, and uterus. Endo- and ectoparasites with prolonged host-tissue contact promote the most dramatic eosinophilia. Endo- and ectoparasites with prolonged host-tissue contact promote the most dramatic eosinophilia.

113. Eosinophilia in birds is unusual and is most frequently observed in raptors. Dietary exposure to parasites may be involved. Eosinophilia in birds is unusual and is most frequently observed in raptors. Dietary exposure to parasites may be involved.

114. Eosinopenia

115. Eosinopenia occurs in response to corticosteroids via cell redistribution in the vasculature. Other proposed mechanisms include inhibition of mast cell degranulation, neutralization of histamine in the circulation, or infiltration of lymphoid tissues subsequent to corticosteroid-associated lympholysis and cytokine release. Eosinopenia occurs in response to corticosteroids via cell redistribution in the vasculature. Other proposed mechanisms include inhibition of mast cell degranulation, neutralization of histamine in the circulation, or infiltration of lymphoid tissues subsequent to corticosteroid-associated lympholysis and cytokine release. Catecholamine (epinephrine) release promotes eosinopenia by adrenergic effect. Catecholamine (epinephrine) release promotes eosinopenia by adrenergic effect.

116. The etiology of eosinopenia in acute infection occurs by a mechanism independent of corticosteroid action. The etiology of eosinopenia in acute infection occurs by a mechanism independent of corticosteroid action. Eosinophils are rare in the blood of avian species other than raptors. Therefore, eosinopenia may be difficult to appreciate clinically. Eosinophils are rare in the blood of avian species other than raptors. Therefore, eosinopenia may be difficult to appreciate clinically.

117. Basophilia

118. An inverse relationship exists between the number of circulating basophils and tissue mast cells. Basophils are rare in the blood of mammals that have a rich tissue mast cell supply. Conversely, basophils are more prominent in avian blood, and tissue mast cells are sparse. An inverse relationship exists between the number of circulating basophils and tissue mast cells. Basophils are rare in the blood of mammals that have a rich tissue mast cell supply. Conversely, basophils are more prominent in avian blood, and tissue mast cells are sparse. Basophilia in mammalian blood smears is seldom dramatic, but observing even a few of these cells on the blood smear usually attracts attention. Basophilia is present when these cells exceed 200-300//lit. Basophilia in mammalian blood smears is seldom dramatic, but observing even a few of these cells on the blood smear usually attracts attention. Basophilia is present when these cells exceed 200-300//lit.

119. Those IgE-generating disorders that cause predictable eosinophilia often have concomitant basophilia. Those IgE-generating disorders that cause predictable eosinophilia often have concomitant basophilia. Basophilia occurs in cats, but it may be overlooked because the granules of mature basophils do not stain metachromatically. The granules usually appear lavender to taupe (brownish-gray) with Romanowsky stains. Basophilia occurs in cats, but it may be overlooked because the granules of mature basophils do not stain metachromatically. The granules usually appear lavender to taupe (brownish-gray) with Romanowsky stains. Basophilia in the absence of eosinophilia is rare, but may be observed occasionally in equine blood smears. Basophilia in the absence of eosinophilia is rare, but may be observed occasionally in equine blood smears.

120. Disorders of lipid metabolism in mammals are not associated with basophilia, as measured by the routine WBC count. The routine WBC count is too crude to quantitate very mild basophilia precisely. Disorders of lipid metabolism in mammals are not associated with basophilia, as measured by the routine WBC count. The routine WBC count is too crude to quantitate very mild basophilia precisely. Basophilia is observed more commonly in avian blood smears, probably because of increased numbers of these cells in health. However, avian basophils may be difficult to identify because their granules may dissolve with Diff-Quik staining. Degranulated basophils have a vacuolated or "moth-eaten" appearance. Basophilia is observed more commonly in avian blood smears, probably because of increased numbers of these cells in health. However, avian basophils may be difficult to identify because their granules may dissolve with Diff-Quik staining. Degranulated basophils have a vacuolated or "moth-eaten" appearance.

121. Basopenia

122. Basopenia is difficult to appreciate clinically unless special stains, diluent, and a hemacytometer are used to perform an absolute basophil count. Basopenia is difficult to appreciate clinically unless special stains, diluent, and a hemacytometer are used to perform an absolute basophil count.

123. Lymphocytosis

124. The number of circulating lymphocytes tends to be quite constant in health and decreases slightly with age in most species; young animals have higher lymphocyte counts. For example, average lymphocyte counts in horses decline from approximately 5,200-3.100//a1 between 8 months and >5 years of age. The number of circulating lymphocytes tends to be quite constant in health and decreases slightly with age in most species; young animals have higher lymphocyte counts. For example, average lymphocyte counts in horses decline from approximately 5,200-3.100//a1 between 8 months and >5 years of age. The epinephrine effect of excited, healthy animals causes lymphocytosis. The epinephrine effect of excited, healthy animals causes lymphocytosis.

125. Antigenic stimulation occasionally causes lymphocytosis: Antigenic stimulation occasionally causes lymphocytosis:

126. Enlarged lymph nodes caused by antigenic stimulation (lymphoid hyperplasia) are commonly encountered in all species, but blood lymphocyte numbers correlate poorly with increased functional reactivity. Enlarged lymph nodes caused by antigenic stimulation (lymphoid hyperplasia) are commonly encountered in all species, but blood lymphocyte numbers correlate poorly with increased functional reactivity. The blood lymphocyte number may be within the reference interval or decreased in association with enlarged lymph nodes, especially during acute stages of infection. The blood lymphocyte number may be within the reference interval or decreased in association with enlarged lymph nodes, especially during acute stages of infection.

127. Reactive lymphocytes (immunocytes) may occur in the blood with or without lymphocytosis. Reactive lymphocytes (immunocytes) may occur in the blood with or without lymphocytosis. During chronic stages of infection, intensifying lymphocytosis (up to 20,000- 30,000/^il) may be seen infrequently (e.g., Rocky Mountain Spotted Fever and canine ehrlichiosis) in dogs. Rickettsial titrs should be evaluated to distinguish reactive lymphocytosis from chronic lymphocytic leukemia. During chronic stages of infection, intensifying lymphocytosis (up to 20,000- 30,000/^il) may be seen infrequently (e.g., Rocky Mountain Spotted Fever and canine ehrlichiosis) in dogs. Rickettsial titrs should be evaluated to distinguish reactive lymphocytosis from chronic lymphocytic leukemia.

128. Persistent lymphocytosis in cattle is a subclinical. Non neoplastic manifestation of bovine leukemia virus infection. Viral infection promotes B lymphocyte hyperplasia; lymphocyte counts typically range from 7,000-15,000/^1. Persistent lymphocytosis in cattle is a subclinical. Non neoplastic manifestation of bovine leukemia virus infection. Viral infection promotes B lymphocyte hyperplasia; lymphocyte counts typically range from 7,000-15,000/^1. Lymphocytosis is common in lymphocytic leukemias and can occur in association with the leukemic blood profile of lymphoma. Lymphocytosis is common in lymphocytic leukemias and can occur in association with the leukemic blood profile of lymphoma. Lymphocyte counts in healthy growing swine are higher than other species, typically 13,000-26,000//xl. Lymphocyte counts rarely exceed reference values in swine. Lymphocyte counts in healthy growing swine are higher than other species, typically 13,000-26,000//xl. Lymphocyte counts rarely exceed reference values in swine.

129. Lymphocytosis may be dramatic in birds with chronic bacterial, viral, fungal, or parasitic infections. Lymphocytosis may be dramatic in birds with chronic bacterial, viral, fungal, or parasitic infections.

132. Lymphopenia

133. Lymphopenia is a common abnormality in the leukogram of sick animals. The mechanism leading to lymphopenia is seldom differentiated before a final diagnosis is made; it may be postulated only in retrospect Lymphopenia is a common abnormality in the leukogram of sick animals. The mechanism leading to lymphopenia is seldom differentiated before a final diagnosis is made; it may be postulated only in retrospect Mechanisms that cause lymphopenia include the following: Mechanisms that cause lymphopenia include the following:

134. Corticosteroid-induced redistribution of recirculating lymphocytes. Corticosteroid-induced redistribution of recirculating lymphocytes. Acute systemic infection. When there is generalized disbursement of infectious antigen, recirculating lymphocytes may be trapped in lymph nodes, which may be enlarged concomitant with lymphopenia. The lymphopenia tends to disappear with time. Acute systemic infection. When there is generalized disbursement of infectious antigen, recirculating lymphocytes may be trapped in lymph nodes, which may be enlarged concomitant with lymphopenia. The lymphopenia tends to disappear with time. Viral infections are more likely to cause lymphopenia than bacterial infections Viral infections are more likely to cause lymphopenia than bacterial infections

135. Local infections may cause entrapment of lymphocytes in the regional lymph nodes, but lymphopenia is unlikely. Local infections may cause entrapment of lymphocytes in the regional lymph nodes, but lymphopenia is unlikely. Acquired T lymphocyte deficiency. Most recirculaling lymphocytes are T-cells. Certain infections in neonates cause thymic necrosis or atrophy; if the animal survives, persistent lymphopenia occurs. Acquired T lymphocyte deficiency. Most recirculaling lymphocytes are T-cells. Certain infections in neonates cause thymic necrosis or atrophy; if the animal survives, persistent lymphopenia occurs. Immunosuppressive therapy or irradiation. These agents suppress clonal proliferation of lymphocytes. Lymphopenia develops slowly. Immunosuppressive therapy or irradiation. These agents suppress clonal proliferation of lymphocytes. Lymphopenia develops slowly.

136. Loss of lymphocyte-rich, efferent lymph. This mechanism of lymphopenia primarily occurs with loss of thoracic duct lymph (i.e., chylothorax). Loss of lymphocyte-rich, efferent lymph. This mechanism of lymphopenia primarily occurs with loss of thoracic duct lymph (i.e., chylothorax). Lymphopenia may occur wilh intestinal lymphangiectasia Lymphopenia may occur wilh intestinal lymphangiectasia

137. Disruption of lymph node architecture by inflammation, infection, or neoplasia that.replaces lymphoid tissue and alters existing patterns of lymphocyte recirculation. Disruption of lymph node architecture by inflammation, infection, or neoplasia that.replaces lymphoid tissue and alters existing patterns of lymphocyte recirculation. Hereditary immunodeficiency. Selective T lymphocyte deficiency is characterized by lymphopenia, and combined T and B lymphocyte (SCID) deficiency has lymphopenia and decreased serum immunoglobulin concentrations. Animals with only B lymphocyte deficiency do not have lymphopenia. Hereditary immunodeficiency. Selective T lymphocyte deficiency is characterized by lymphopenia, and combined T and B lymphocyte (SCID) deficiency has lymphopenia and decreased serum immunoglobulin concentrations. Animals with only B lymphocyte deficiency do not have lymphopenia.