What is CSF?

Cerebrospinal fluid (CSF) is a normally clear, colorless fluid that bathes the brain and spinal cord. The fluid is formed primarily from secretions by the choroid plexus into the ventricles of the brain and, to a lesser extent, from excretions from ependymal cells. It contains glucose, electrolytes, amino acids, and other small molecules found in plasma, but has very little protein and few cells. CSF protects the central nervous system from injury, cushions it from the surrounding bone structure, provides it with nutrients, and removes waste products by returning them to the blood.1

Cell Counts: Why the Test is Performed

The indications for collecting CSF include four major categories of disease: 1) meningeal infection, 2) subarachnoid hemorrhage, 3) central nervous system malignancy, and 4) demyelinating disease2.

How CSF is Collected

Most commonly, CSF is collected by lumbar puncture. In some cases, lateral cervical puncture, ventricular puncture, or cisternal puncture may be utilized2. Typically, CSF is collected into 3-4 sterile tubes without anticoagulant. Generally, the first tube is used for chemical and/or serological analysis and the last two tubes are used for microbiology/hematology tests. The fourth tube may be utilized for cytology or other specialized testing. This reduces the chances of recording falsely elevated red and white cell counts caused by a traumatic tap, as well as contamination of the microbiology culture by skin flora.1

CSF Stability

Cell counts should be performed as soon as possible after collection due to the instability of cellular constituents. Delayed testing can cause inaccurate results.3

References

1Brunzel, N.A. (2013). Fundamentals of Urine & Body Fluid Analysis (Third ed.). St. Louis, Missouri: Elsevier Saunders; 314, 316, 318-320.

2Hussong, J.W., Kjeldsberg, C.R. (2015). Body Fluids Analysis (Third ed.). Chicago, Illinois: American Society of Clinical Pathologists; 46-47, 51-52.

3Clinical and Laboratory Standards Institute. Body Fluid Analysis for Cellular Composition; Approved Guidelines. CLSI document H56-A [ISBC 1-56238-614-X]. Clinical and Laboratory Standards Institute, 940 West Valley Road, Suite 1400, Wayne, Pennsylvania 19087-1898 USA, 2006.