The Test Sample
Cerebrospinal fluid (CSF) is a clear watery liquid that is formed and secreted by the choroid plexus, a special tissue that has many blood vessels and that lines the small cavities or chambers (ventricles) in the brain. CSF flows around the brain and spinal cord, surrounding and protecting them. It is continually produced, circulated, and then absorbed into the blood system. About 17 ounces (500 mL) are produced each day. This rate of production means that all of the CSF is replaced every few hours. A CSF analysis is a group of tests that evaluate substances present in CSF in order to diagnose conditions affecting the central nervous system.
- CSF color, clarity and pressure during collection
- CSF protein
- CSF glucose
- CSF cell count (total number of cells present)
- CSF differential cell count (numbers of different types of cells present)
- If infection is suspected, CSF gram stain and culture
- Physical characteristics —includes measurement of the pressure during sample collection and the appearance of the CSF.
- Chemical tests —this group refers to those tests that detect or measure the chemical substances found in spinal fluid. Many of the substances in CSF are also in blood and the relative amounts in CSF and blood are often compared. Normally, levels of certain constituents of CSF, such as protein and glucose, are reflective of their concentration in the blood.
- Microscopic examination (Cell count and differential)—any cells that may be present are counted and identified by cell type under a microscope.
- Infectious disease tests —numerous tests can be done to detect and identify microorganisms if an infection is suspected.