Curriculum · Neurology
Interpretation of CSF analysis
What it is
CSF analysis will tell you one thing and will not tell you another. It will tell you whether the picture is bacterial or viral, and it does that on four parameters. It will not tell you the type of bacteria or virus; that comes from the history and from the CSF culture.
How it is diagnosed
The normal values are an opening pressure of 5-20, leukocytes under 5, a cell differential of 0, protein 15-45 and glucose 45-85. A second table sets normal against bacterial and against nothing else. There the normal protein is put at less than 0.5 g/dl, the glucose at 2.6-4.5 mmol and the CSF to plasma glucose ratio above 0.66, while the bacterial side reads WBCs above 100 to 5000 or more, neutrophil predominance, raised protein, very low glucose and a very low CSF to plasma glucose ratio.
The other four settings:
- Bacterial: opening pressure elevated, leukocytes above 1,000, neutrophil predominance, protein high, glucose low, cultures positive.
- Viral: opening pressure normal or slightly elevated, leukocytes 25-2,000, lymphocyte predominance, protein high, glucose low or normal, cultures negative.
- Fungal: opening pressure elevated, leukocytes 10-1,000, lymphocyte predominance, protein high, glucose low, cultures positive for fungal.
- Tuberculosis: opening pressure variable, leukocytes 10-1000, lymphocyte predominance, protein very high, glucose low, cultures positive for AFB.
A further table sets viral against bacterial meningitis with the values written out. In viral meningitis the opening pressure is ≤250 mm H2O, the leukocyte count 50-1000, the predominance is of lymphocytes, glucose is above 45 mg/dL or 2.5 mmol/L, protein is under 200 mg/dL, and Gram stain and culture are both negative. In bacterial meningitis the opening pressure is 200-500 mm H2O, the leukocyte count 1000-5000, the predominance is of neutrophils, glucose is under 40 mg/dL or 2.2 mmol/L, protein is 100-500 mg/dL, Gram stain is positive in 60%-90% and culture is positive in 70%-85%. Two notes are set beside that bacterial side: TB and brucella = lymphocytes, and the glucose is Normal in Brucella.
The CSF is also read outside infection: in transverse myelitis it shows pleocytosis and an elevated IgG index.