1. Cerebrospinal, Synovial, and Serous Body Fluids

2. Indication
Appropriate laboratory examination of these fluids is critical for the diagnosis of numerous diseases
(i.e., bacterial, viral and fungal infections; distinction between various arthritides; primary [i.e., mesothelioma ] and metastatic malignancies; among others).

3. Accurate test interpretation depends on appropriate specimen collection, turnaround time, physician/laboratory communication, and reliable reference values.

4. Cerebrospinal Fluid
In adults, approximately 500 mL of cerebrospinal fluid (CSF)is produced each day ( mL/min).
The total adult volume varies from mL,
about 25 mL of which is in the ventricles and the remainder in the subarachnoid space.
In neonates, the volume varies from mL.
The total CSF volume is replaced every 5-7 hours

5. CSF functions Several major functions:
(a) it provides physical support since the 1500 g brain weighs about 50 g when suspended in CSF;
(b) it confers a protective effect against sudden changes in acute venous (respiratory and postural) and arterial blood pressure or impact pressure;

6. CSF functions
(c) it provides an excretory waste function since the brain has no Iymphalic system;
(d) it is the pathway whereby hypothalamus releasing factors are transported to the cells of the median eminence;
(e) it maintains central nervous system ionic homeostasis .

7. BBB The blood-brain barrier
It consists of two morphologically distinct components:
a unique capillary endothelium held together by intercellular tight junctions,
&
the choroid plexus, where a single layer of specialized choroidal ependyma cells connected by tight junctions overlies fenestrated capillaries.

8. The CSF ionic components
(e.g., H+, K+, Ca2+, Mg2+,bicarbonate, etc.) are tightly regulated by specific transport systems,
Glucose, urea, and creatinine diffuse freely but require 2 or more hours to equilibrate.
Proteins cross by passive diffusion at a rate dependent on the plasma-to-CSF concentration gradient and inversely proportional to their molecular weight and hydrodynamic volume

9. the BBB maintains the relative homeostasis of the central nervous system environment during acute perturbations of plasma components.

10. Specimen Collection
Cerebrospinal fluid may be obtained by lumbar puncture
Up to 20 mL of CSF may normally be removed
the clinician should be aware of the clinical history
The sample site (i.e., lumbar, cisternal, etc.) should be noted since cytologic and chemical parameters vary at different sites

11. The necessity for a simultaneous serum glucose should also be considered. This is best obtained 2-4 hours before lumbar puncture because of the delay in serum-CSF equilibrium.
The CSF specimen is usually divided into three serially collected sterile tubes:
tube 1 for chemistry and immunology studies;
tube 2 for microbiologic examination;
tube 3 for cell count and differential.

12. if tube 1 is hemorrhagic due to a traumatic puncture, it should not be used when protein studies are the most important aspect of the analysis (i.e., suspected multiple sclerosis).
Glass tubes should be avoided
Specimens should be delivered to the laboratory and processed quickly to minimize cellular degradation (<1 h)

13. Refrigeration is contraindicated for culture Specimens
because fastidious organisms (e.g., Haemophilus influenzae and Neisseria meningitidis) will not survive.

14. Indications and Recommended Tests
four major disease categories:
Meningeal infection, subarachnoid hemorrhage, primary or metastatic malignancy, and demyelinating diseases
Identification of infectious meningitis, particularly bacterial, is the most important indication for CSF examination

15. Diseases Detected by Laboratory Examination of CSF

16. CSF examination for other diseases
often provides supportive evidence of a clinical diagnosis or helps to rule out other diseases.

17. Recommended CSF Laboratory Tests

18. Gross Examination
Normal CSF is crystal clear and colorless and has a viscosity similar to that of water.
Turbidity or cloudiness
leukocyte (WBC) counts over 200 cells/μL
red cell (RBC) counts of 400/ μL. However, grossly bloody fluids have RBC counts greater than 6000/ μL.
Microorganisms (bacteria, fungi, amebas),
Radiographic contrast material,
Aspirated epidural fat
Protein level greater than 150 mg/dL (1.5 g/L)

19. Xanthochromia and Associated Diseases/Disorders

20. Xanthochromia
To detect xanthochromia, the CSF should be centrifuged and the supernatant fluid compared with a tube of distilled water.
Xanthochromic CSF is pink, orange, or yellow owing to RBC lysis and hemoglobin breakdown.

21. Differential Diagnosis of Bloody CSF
Distinction of a traumatic puncture from pathologic hemorrhage
In a traumatic tap, the hemorrhagic fluid usually clears between the first and third collected tubes, but remains relatively uniform in subarachnoid hemorrhage.
Xanthochromia, microscopic evidence of erythrophagocytosis, or hemosiderin-laden macrophages indicate a subarachnoid bleed

22. Microscopic Examination
Total Cell Count

23. The normal leukocyte cell count
adults , 0-5 cells/μL.
It is higher in neonates, ranging from 0-30 cells/μL. with the upper limit of normal decreasing to adult values by adolescence.
No RBCs should be present in normal CSF.
If numerous (except a traumatic tap), a pathologic process is probable (e.g., trauma, malignancy, infarct, hemorrhage).

24. Red cell counts have limited diagnostic value, they may give a useful approximation of the true CSF white blood count (WBC) or total protein in the presence of a traumatic puncture by correcting for leukocytes or protein introduced by the traumatic puncture.

25. In the presence of a normal peripheral blood RBC count and serum protein, these corrections amount to about 1 WBC for every 700 RBCs and 8 mg/dL protein for every RBC/μL.

26. Differential Cell Count
Wright's staining of air-dried cytospins. Indeed, it is the recommended method for differential cell counts in all body fluids

27. Causes of Increased CSF Neutrophils

28. Causes of CSF Lymphocytosis

29. Chemical Analysis
Adult Lumbar CSF Reference Values

30. Proteins
Over 80% of the CSF protein content is derived from blood plasma, in concentrations of less than 1% of the plasma level
it is the most common abnormality found in CSF.
an increased CSF protein serves as a useful, albeit nonspecific, indicator of meningeal or CNS disease.

31. Mean Concentrations of Plasma and CSF Proteins

32. infants have significantly higher CSF protein levels than older children and adults.

33. Conditions Associated with Increased CSF Total Protein

34. CSF Proteins and Central Nervous System Diseases

35. Glucose
fasting CSF glucose levels are normally mg/dL( mmol/L), about 60% of plasma values
The normal CSF/plasma glucose ratio varies from
CSF values below 40 mg/dL (2.2 mmol/L) or ratios below 0.3 are considered to be abnormal.

36. Hypoglycorrhachia is a characteristic finding of bacterial, tuberculous, and fungal meningitis. However, sensitivity can be as low as 55% for bacterial meningitis
Decreased CSF glucose results from increased anaerobic glycolysis in brain tissue and leukocytes and impaired transport into the CSF.

37. CSF glucose levels normalize before protein levels and cell counts during recovery from meningitis, making it a useful parameter in assessing response to treatment.
Increased CSF glucose is of no clinical ignificance, reflecting increased blood glucose levels within 2 hours of lumbar puncture. A traumatic tap may also cause a spurious increase in CSF glucose.

38. Typical Lumbar CSF Findings in Meningitis

39. Microbiological Examination
A thorough and prompt examination of cerebrospinal fluid is essential for the diagnosis of CNS infection because an inaccurate or delayed report may result in significant mortality or morbidity. Although changes in opening pressure, total cell and differential counts, total protein, and glucose suggest an infectious etiology, Gram stain and culture are critical for a definitive diagnosis.

40. The most common agents of bacterial meningitis
are group B streptococcus (neonates), Neisseria meningitidis (3 months and older) ,Streptococcus pneumoniae (3 months and older), Escherichia coli and other Gram.negative bacilli (newborn to 1 month),Haemophilm influenzae (3 months to 18 years) and Listeria monocyLDgenes
(neonates, elderly, alcoholics, & immunosuppressed)

41. Synovial Fluid
(SF)
an imperfect ultrafiltrate of blood plasma combined with hyaluronic acid produced by the synovial cells.
Small ions and molecules (e.g., Na+, K+, glucose, urea, etc.) readily pass into the joint space and are, therefore, similar in concentration to plasma,
Large molecules
absent or present in trace amounts. Resorption of synovial molecules is by the lymphatics and is not size dependent.
SF acts as a lubricant and adhesive, and provides nutrients for the avascular articular cartilage.

42. Examination of the synovial fluid
is essential to
Distinguish infectious from noninfectious arthritis.
Gross and microscopic examination
Gram stain, culture, and crystal examination
Synovial fluid parameters can be nonspecific and must be integrated into the clinical context.

43. Synovial Fluid Findings by Disease Category

44. Specimen Collection
Synovial fluid must be collected with sterile, disposable needles and plastic syringes to avoid contamination by birefringent particulates. The syringe may be heparinized with 25 U of sodium heparin/mL of SF in routine arthrocentesis.
Oxalate, lithium heparin, and powdered ethylenediaminetetraacetic acid (EDTA) anticoagulants should be avoided because they form crystal artifacts that may be misleading during the microscopic examination.
Prior to aspiration, turn or manipulate the joint to ensure mixing of its contents.

45. Specimen Collection
The specimen should ideally be separated into three parts:
3-10 mL into a sterile heparinized tube or syringe for microbiological studies;
2-5 mL in an anticoagulant tube (sodium heparin or liquid EDTA) for microscopic examination;
about 5 mL into a plain (no anticoagulant) tube for chemical analysis (normal synovial fluid does not clot since fibrinogen is absent).

46. Recommended Tests

47. Crystals Monosodium urate Calcium pyrophosphllte dihydrate
Calcium Hydroxyapatites
Calcium oxalate dihydrare
Lipid crystals
Crystalline corticosteroids
Cholesterol crystals

48. Reference Intervals for Synovial Fluid Constituents