CBC Basic Interpretation Tanim I. Aziz, MBBS

CBC… is one of the most common laboratory tests in medicine. Typically, it includes the following: White blood cell count (WBC or leukocyte count) WBC differential count Red blood cell count (RBC or erythrocyte count) Hematocrit (Hct) Hemoglobin (Hb) Mean corpuscular volume (MCV) Mean corpuscular hemoglobin (MCH) Mean corpuscular hemoglobin concentration (MCHC) Red cell distribution width (RDW) Platelet count Mean Platelet Volume (MPV)

How does CBC come ?

Circulating blood cells, including red blood cells (RBCs), white blood cells (WBCs), and platelets, are counted and sized electronically by modern instruments. One such instrument, the Coulter counter, generates an electrical pulse when a blood cell passes through a small aperture surrounded by electrodes. Each electrical pulse represents an individual cell, and the pulse height indicates the cell volume. Therefore, the electronic counter not only registers the total cell count but also estimates the average cell volume and the variation in cell size. In the context of RBCs, these measurements are referred to as the mean corpuscular volume (MCV) and the RBC distribution width, respectively.

Modern electronic counters are also capable of multimodal assessment of cell size and content, thus providing additional information about the various categories of WBCs including neutrophils, lymphocytes, monocytes, eosinophils, and basophils (ie, 5-part differential). Two other “measured variables” of the complete blood cell count (CBC) are hemoglobin (Hgb) and hematocrit (Hct). The Hg is computed by a spectrophotometer after RBCs are lysed in a given volume of blood and the Hgb is chemically converted into a stable pigment.

The Hct is determined by a microhematocrit centrifuge and represents the percentage of a given volume of whole blood that is occupied by packed RBCs. However, Hct also can be calculated by multiplying the RBC count and the MCV. Other “calculated” variables in the CBC include the mean corpuscular Hg content (and mean corpuscular Hg concentration; these 2 calculated values are rarely used in routine clinical practice.

ANEMIA Microcytic (MCV <80 fL) Normocytic (MCV fL) Macrocytic (MCV >100 fL)

MICROCYTIC ANEMIA The 3 major diagnostic possibilities for microcytic amaenia are : Iron deficiency anemia (IDA), Thalassemia, Anemia of chronic disease (ACD)

IDA RBC: normal or low Hb: low MCV: low RDW: high

Thalassemia RBC: normal or high Hb: low MCV: low RDW: normal Disproportionate !!! An extremely low MCV may suggest Alpha – thalassemia !!!

The CBC count and peripheral blood film examination results are usually sufficient to suspect the diagnosis. In the severe forms of thalassemia, the Hb level ranges from 2-8 g/dL. MCV and MCH are significantly low, but, unlike thalassemia trait, thalassemia major is associated with a markedly elevated RDW, reflecting the extreme anisocytosis. The WBC count is usually elevated in b thalassemia major; this is due, in part, to miscounting the many nucleated RBCs as leukocytes. Platelet count is usually normal, unless the spleen is markedly enlarged.

Mentzer index Is used to differentiate IDA from B- thalassemia. MCV / RBC : is < 13, thalassemia is more likely. If the result > 14, then iron-deficiency anemia is more likely.

ACD RBC: normal or low ? Hb: low MCV: normal RDW: normal

Macrocytosis Common causes: Drug-induced Nutritional Liver disease, alcohol use Hypothyroidism

Macrocytosis RBC: normal Hb: normal or low MCV: high RDW: normal or high

WBC Leukopenia…. Leukocytosis…. Lots of differentials….do not forget to match with the clinical features presented…

Common causes: Chemotherapy Radiation therapy Leukemia (as malignant cells overwhelm the bone marrow) Myelofibrosis Aplastic anema Medications –Clozapine (anti-psychotic) –Immunosuppressive drugs –Interferons Leucopenia

Other causes : Influenza Systemic lupus erythematosus Typhus Malaria HIV Tuberculosis Dengue Rickettsial infections Enlargement of the spleen Folate deficiencies Psittacosis Sepsis

It can develop upon the onset of infection. The leukocytes are marginalized in the blood vessels so that they can scan for the site of infection. This means that even though there is increased WBC production, it will appear as though it is low from a blood sample, since the blood sample is of core blood and does not include the marginalized leukocytes. Valproic Acid… Pseudoleukopenia

Leukocytosis Neutrophil leucocytosis (neutrophilia >7.5x10 9 /l): Infection:acute bacterial infection Inflammation / necrosis: myocardial infarction or ischaemia trauma vasculitis Myeloproliferative disorders: polycythaemia rubra vera myelofibrosis chronic granulocytic (myelomonocytic) leukaemia Metabolic:uraemia / acidosis gout eclampsia Malignancy:any other malignancy Drugs:steroids Blood loss:acute haemorrhage or haemolysis

Lymphocytosis: Acute viral infection (usually associated with neutropaenia): rubella pertussis mumps infectious mononucleosis most other acute viral illnesses Chronic viral infection:hepatitis B and C Bacterial infections:tuberculosis brucellosis whooping cough acute bacterial infections in infants Other causes:thyrotoxicosis autoimmune disorders lymphoma lymphocytic leukaemias

Thrombocytopenia Decreased production –Vitamin B12 or folic acid deficiency –Leukemia –Decreased production of thrombopoietin –Sepsis, systemic viral or bacterial infection –Hereditary syndromes Congenital amegakyrotic thrombocytopenia Thrombocytopenia absent radius syndrome Fanconi anemia Bernard-Soulier syndrome associated with large platelets Meg-Hegglin anomaly Grey platelet syndrome Alport syndrome

Increased destruction –Idiopathic thrombocytopenic purpura (ITP) –Thrombotic thrombocytopenic purpura (TTP) –Hemolytic-uremic syndrome (HUS) –Disseminated intravascular coagulation (DIC) –Paroxysmal nocturnal hemoglobinuria (PNH) –Antiphospholipid syndrome –Systemic lupus erythematosus (SLE) –Post-transfusion purpura –Neonatal alloimmune thrombocytopenia (NAITP) –Hypersplenism –Dengue fever –HIV

Thrombocytosis Do not necessarily signal any clinical problems, and are picked up on a routine full blood count. A full medical history must be elicited to ensure that the increased platelet count is not due to a secondary process. Thrombopoetin…an acute phase reactant…

Thrombocytosis Essential (primary) –Essential thrombocytosis (a form of myeloproliferative disease) –Other myeloproliferative disorders such as chronic myelogenous leukemia, polycythemia vera, myelofibrosis Reactive (secondary) –Inflammation –Surgery (which leads to an inflammatory state) –Hyposplenism / spleenectomy

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