A few routine tests are usually performed on CSF samples.
- CSF glucose – normal is about 2/3 the concentration of blood glucose. Glucose levels may decrease when cells that are not normally present use up (metabolize) the glucose. These may include bacteria or cells present due to inflammation (white blood cells) or shed by tumors.
- CSF protein – only a small amount is normally present in CSF because proteins are large molecules and do not cross the blood/brain barrier easily. Decreases in CSF protein are not generally considered significant. Increases in protein are most commonly seen with:
If any of the initial tests are abnormal or if the healthcare provider has reason to suspect a specific condition, then additional testing may be ordered. This may include one or more of the following:
- CSF protein electrophoresis — separates different types of protein. Oligoclonal bands may be seen with multiple sclerosis and Lyme disease.
- CSF IgG (Immunoglobulin G) — increased in some conditions, such as multiple sclerosis, herpes encephalitis, connective tissue diseases.
- Myelin basic protein — seen when the covering of nerves (myelin) breaks down, such as with multiple sclerosis.
- CSF lactic acid — often used to distinguish between viral and bacterial meningitis. The level will usually be increased with bacterial and fungal meningitis while it will remain normal or only slightly elevated with viral meningitis.
- CSF lactate dehydrogenase (LD) — used to differentiate between bacterial and viral meningitis; the level is usually increased with bacterial meningitis and not with viral meningitis; may also be elevated with leukemia or stroke.
- CSF glutamine — may be increased with liver disease, hepatic encephalopathy or Reye syndrome
- CSF C-reactive protein (CRP) is an acute phase reactant and is elevated with inflammation. It is markedly increased with bacterial meningitis. Since it is very sensitive even with early bacterial meningitis, it is often used to distinguish between bacterial and viral meningitis.
- Tumor markers — Carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), and hCG may be increased in cancers that have spread from other sites in the body (metastatic).
- Amyloid beta 42 (Aß42) and tau protein—used in the evaluation of Alzheimer disease. In a symptomatic person, a low Aß42 CSF level along with a high tau level reflects an increased likelihood of Alzheimer disease.