MLT GlobeUrinalysis & Body Fluids: CSF
40 Urinalysis & Body Fluids MCQs on CSF with answers and explanations.
CSF with many neutrophils, high protein and glucose below 40% of the blood level suggests:
Bacteria and neutrophils consume glucose and damage the blood-brain barrier, raising protein. Viral meningitis shows lymphocytes with near-normal glucose.
Three CSF tubes are collected in order. Which is the usual assignment of tubes 1, 2 and 3?
Tube 1 goes to chemistry/serology, tube 2 to microbiology and tube 3 to hematology, because the last tube is least likely to contain blood or skin contaminants from the puncture.
Normal CSF glucose is approximately what fraction of the plasma glucose?
CSF glucose is normally about 60–70% of plasma glucose, so a plasma sample should be drawn at the same time. A ratio below about 0.4 suggests bacterial, fungal or TB meningitis.
The normal adult CSF white cell count and main cell types are:
Adult CSF normally has up to 5 WBCs/µL, mainly lymphocytes with some monocytes. Neonates have higher counts (up to about 30/µL) with more monocytes.
The reference range for total protein in adult lumbar CSF is approximately:
Normal lumbar CSF protein is about 15–45 mg/dL, much lower than plasma protein (60–80 g/L). Newborns have higher values.
The total volume of CSF in an adult and its approximate daily production are:
Adults have about 90–150 mL of CSF, produced mainly by the choroid plexus at about 500 mL per day, so it is replaced several times daily.
CSF cell counts should be performed within about 1 hour of collection because:
Cells, especially neutrophils, start to disintegrate in CSF within about an hour, falsely lowering counts. Glucose loss affects chemistry, not the cell count.
Cerebrospinal fluid is produced mainly by the:
Most CSF is secreted by the choroid plexus in the brain ventricles. Arachnoid villi (granulations) reabsorb CSF into the venous sinuses.
Normal cerebrospinal fluid looks:
Normal CSF is crystal clear and colourless, like water. Cloudiness, blood or yellow colour are abnormal findings.
A lumbar puncture in an adult is usually performed between which vertebrae?
The needle is inserted below the end of the spinal cord (about L1–L2 in adults), usually at L3–L4 or L4–L5, to avoid injuring the cord.
Which traditional stain is used on CSF to show the capsule of Cryptococcus neoformans?
India ink provides a dark background so the unstained polysaccharide capsule of Cryptococcus appears as a clear halo. Cryptococcal antigen testing is more sensitive.
A cloudy (turbid) CSF is most often caused by:
Turbidity usually results from many white cells (as in bacterial meningitis), and also from bacteria, red cells or high protein.
Which diluting fluid is used for a manual CSF white cell count because it lyses red cells?
Dilute (3%) acetic acid lyses red cells and makes white cell nuclei easier to see, so WBCs can be counted in a bloody sample. Saline preserves red cells.
Gram-negative diplococci seen in the CSF of a young adult with meningitis and a rash are most likely:
Neisseria meningitidis appears as Gram-negative kidney-shaped diplococci and often causes a petechial or purpuric rash. S. pneumoniae is a Gram-positive diplococcus.
CSF from a lumbar puncture is bloody in tube 1 and becomes clearer in tubes 2 and 3. The supernatant is clear and colourless. This most suggests:
A falling red cell count from tube 1 to 3 with a clear supernatant indicates blood introduced by the needle. Subarachnoid hemorrhage gives evenly bloody tubes and, after some hours, xanthochromia.
A 22-year-old with headache and neck stiffness has CSF: WBC 180/µL (85% lymphocytes), glucose 62 mg/dL (plasma 95 mg/dL), protein 70 mg/dL. The most likely diagnosis is:
Moderate lymphocytic pleocytosis, normal glucose ratio (about 0.65) and mildly raised protein fit viral meningitis. TB meningitis would show a low glucose and much higher protein.
CSF left standing forms a delicate web-like clot (pellicle). Cell count shows lymphocytes, glucose is low and protein is markedly raised. This most suggests:
TB meningitis typically has lymphocytes, low glucose, very high protein and a pellicle from fibrinogen. Viral meningitis has normal glucose, and Guillain–Barré shows high protein with few cells.
An HIV-positive patient has chronic headache. Which CSF test is most sensitive for cryptococcal meningitis?
Cryptococcal antigen tests (latex agglutination or lateral flow) are more sensitive than India ink, which shows encapsulated yeast in only some cases. Gram stain is poor for Cryptococcus.
A cytocentrifuge CSF slide from a child being treated for acute lymphoblastic leukemia shows large cells with fine chromatin and nucleoli. This indicates:
Blasts in CSF indicate CNS leukemia, which changes treatment. Choroid plexus and ependymal cells appear in clusters and have uniform, mature nuclei.
Increased CSF myelin basic protein is mainly a marker of:
Myelin basic protein is released when myelin is damaged, as in multiple sclerosis relapses or other demyelinating injury. It does not show where IgG is made.