CSF Analysis Lecture PDF

Analysis of the cerebrospinal fluid CSF is a clear, colorless fluid, found around and inside the brain and spinal cord. It is composed of about 99% water. CSF is produced by selective dialysis of blood plasma by the choroid plexus of brain ventricles and brain capillaries. CSF mo...

Analysis of the cerebrospinal fluid CSF is a clear, colorless fluid, found around and inside the brain and spinal cord. It is composed of about 99% water. CSF is produced by selective dialysis of blood plasma by the choroid plexus of brain ventricles and brain capillaries. CSF moves in and around all the major structures of the brain The total volume of CSF is about 150 ml and the rate of CSF production is about 550 ml/day thus, turnover rate is about 3.7 times a day. Functions of the CSF include: 1. Removal of waste products from the brain and CNS. 2. Transport of biologically active compounds. 3. Physical support and protection of the CNS from trauma. 4. Supplying nutrients to the CNS. CSF analysis is required in diagnosis of: 1. Infections of the brain and spinal cord: as meningitis. 2. Autoimmune disorders: as multiple sclerosis. 3. Bleeding in the brain. 4. Brain tumors. 5. Cerebral dysfunction: e.g. Alzheimer’s disease. Total CSF volume: Adult 85 - 150 ml. Neonate 10 - 60 ml. Rate of formation in adult: 500 ml/day. Turnover = 20 ml/hour. CSF is collected by lumbar puncture in which a fine bore needle is passed between the 3rd and 4th lumber vertebrae into the subarachnoid space with the patient lying in the lateral position and the fluid allowed to flow automatically. The whole procedure is done under strict asepsis. The first few drops of the fluid are discarded and the rest of the fluid is “collected in sterile containers. Up to 20 ml can be taken from an adult, if pressure is normal (50-180 mm Hg) and placed into sterile tubes. Composition of CSF: CSF analysis: CSF glucose concentration is 60% of serum. Ratio of serum: CSF protein is 200:1. Na+, Cl- and Mg2+ are same or greater than serum but K+ and Ca2+ are lower than serum. Active transport is responsible for maintaining this difference. The specimen is divided into 3 aliquots for: Physical examination: volume, appearance. 1. Biochemical investigations: a. Total proteins: Lowry method or turbidometry. b. Determination of glucose. c. Chloride determination. d. Enzymes (LDH, CK). e. Determination of lactate, chloride, bicarbonates, urea, calcium, copper, folate. f. Glutamine for hepatic encephalopathy in liver failure. 2. Microscopic examination: e.g. WBCs, RBCs, cancer cells. 3. Microbiological investigations: staining of centrifuged deposit with Gram stain, culture and sensitivity. Cerebrospinal fluid has no normal microbial flora. CSF analysis: I. Physical analysis: 1. Appearance: normal CSF is clear and colorless and gives no sediment on standing. 2. Color: Red color: blood due to bleeding in hemorrhage. Pink: RBC’s breakdown. Yellow color: jaundice, high protein levels >150mg/dL. Green: hyperbiliruminemia , bacterial meningitis. 3. Viscosity: is equal to water in normal CSF, increased with increased proteins. 4. Turbidity: CSF may clot if the ratio of blood to CSF is high. Usually due to fibrin clot. Presence of >200WBC’s or >400 RBC’s, bacterial meningitis, etc. II. Biochemical analysis: 1. Proteins in CSF: Normally, CSF proteins originate from serum and reach the cerebral space by endocytosis across the capillary endothelium. Increased CSF protein occurs in: 1. Subarachnoid hemorrhage. 2. Infection. 3. Inflammation. 4. Bacterial, viral, or fungal meningitis. 5. Dehydration. 6. Trauma. 7. Diabetic neuropathy. 8. Tumors. 9. Autoimmune diseases. 2. Glucose: Glucose is the main source of energy for the brain. CSF glucose level is 60% of the normal plasma glucose. Blood and CSF glucose equilibrate after 4 hours so that CSF glucose at a given time reflects the BGL during the past 5 hr. When glucose determination is critical, the patient should fast for 4 hr. Decreased glucose level in: 1. Acute bacterial meningitis. 2. Subarachnoid hemorrhage. 3. Hypoglycemia. 4. Malignant tumors. Increased glucose level in: Diabetic hyperglycemia. Interpretation of results: Bacterial Viral Tuberculous Brain Tumor Meningitis Meningitis Meningitis Protein Increased Normal Increased Increased Normal Glucose Decreased or Decreased Decreased slightly affected Glucose will be rapidly destroyed in the absence of preservatives. After drawing the CSF sample, the analysis of glucose and proteins should be carried out immediately. Otherwise, the specimen must be stored at -20C which is stable for 3 days.  Equilibrated CSF glucose of 40mg/dl is abnormal. i.e. less than 40% of simultaneously determined BGL. Decreased CSF glucose (Hypoglycorrachia) occurs in meningitis, infections, tumors, etc. – Note: streptomycin used in the treatment of tuberculous meningitis can reduce the alkaline copper reagent that is used in glucose determination. Elevated CSF glucose occurs in hyperglycemia. Determination of proteins in CSF:several methods, example: I ml CSF + 4ml coomassie Brilliant Blue G-250 reagent + Add 2.5ml of 1M NaOH, mix. keep for 10 min. then read at 595nm. Determination of glucose in CSF: estimated as BGL or by: 0.1ml of CSF + 7.8ml of isotonic solution in a centrifuge tube + 0.1ml sodium tungstate solution. Mix and centrifuge at 2000 rpm for 10 min. 2ml each of the supernatant + 2ml of alkaline copper sulfate, heat in boiling water for 10 min, cool and add 2ml of arseno- molybdic acid reagent, wait for 5 min. then read at 540 nm. Estimation of chlorides in CSF: 1ml CSF + 5 drops of 5% potassium chromate, then titrate against AgNo3 (0.29%) till end point lemon yellow. Reading in ml. x 1000 = mg% chloride. III. Microscopic examination: Cell count: WBCs and RBCs in the CSF. Increased WBCs may indicate infection. Increased RBCs may suggest bleeding. Differential cell count: to identify the cause of inflammation Normal cell count: < 5 WBC’s/mm in adults, and < 20 WBC’s/mm in newborns (70% lymphocytes, 30% monocytes). Patients with bacterial meningitis have >100 WBC’s/mm (less than that is common for viral meningitis). Viral meningitis: predominance of T lymphocytes. Bacterial meningitis: predominance of PMN’s. Fungal and tubercular meningitis: predominance of lymphocytes. IV. Microbiological tests: For diagnosis of infections affecting the CNS such as meningitis. To identify the specific pathogen causing the infection, allowing for targeted treatment. Culture for bacteria or fungi from the CSF sample. Gram stain. Polymerase chain reaction (PCR): to detect the genetic material of specific microorganisms.