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 (metabolise) the glucose. These may include bacteria or cells present due to inflammation (WBCs) or shed by tumours.
- 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 doctor has reason to suspect a specific condition, then additional testing may be requested. 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.
- 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; may also be elevated with leukaemia or stroke.
- CSF amino acid analysis – may be requested in the investigation of several inherited metabolic diseases, particularly those presenting with unexplained seizures
- CSF bilirubin – seen following subarachnoid haemorrhage (SAH). Requested when SAH is suspected but evidence of a bleed has not been demonstrated by a computed tomography (CT) scan