What is Glucose-Cerebrospinal Fluid?

Also Known As: CSF Analysis, Spinal Fluid Analysis

Formal Name: Cerebrospinal Fluid Analysis

Cerebrospinal fluid (CSF) is a clear, watery liquid that flows around the brain and spinal cord, surrounding and protecting them. CSF testing is performed to evaluate the level of concentration of different substances and cells in CSF in order to diagnose conditions affecting the brain and spinal cord (central nervous system).

CSF is produced 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. The total CSF volume is 3-5 ounces (90-150 mL) in adults and 0.3-2 ounces (10-60 mL) in newborns. CSF is continually produced, circulated, and then absorbed into the blood. About 17 ounces (500 mL) of CSF are produced each day. This rate of production means that all the CSF is replaced every few hours.

A protective, semi-permeable barrier separates the brain from the bloodstream. This blood-brain barrier allows some substances to cross and prevents other substances from crossing. Importantly, it helps keep large molecules, toxins, and most blood cells away from the central nervous system. Any condition that disrupts this protective barrier may result in a change in the normal level or makeup of CSF. Because CSF surrounds the brain and spinal cord, testing a sample of CSF can be very valuable in diagnosing a variety of conditions affecting the central nervous system.

Although a sample of CSF may be more difficult to obtain than, for example, urine or blood, the results of CSF testing may reveal more directly the cause of central nervous system conditions. The following are some examples:

• Meningitis, an infection of the layers that cover the brain and spinal cord (meninges), and encephalitis, an infection in the brain
• Autoimmune diseases that affect the central nervous system, such as multiple sclerosis
• Cancers of the central nervous system or cancers that have spread to the central nervous system, such as leukemia
• Alzheimer disease, an irreversible form of dementia

How is the test used?

Cerebrospinal fluid (CSF) testing may be used to help diagnose a wide variety of diseases and conditions affecting the brain and spinal cord (central nervous system). Some examples include:

• Infections, such as meningitis and encephalitis—testing is used to determine if the infection is caused by bacteria, viruses or, less commonly, by Mycobacterium tuberculosis, fungi or parasites, and to distinguish them from other conditions. CSF testing may also be used to detect infections of or near the spinal cord.
• Bleeding (hemorrhaging) around the brain
• Autoimmune disorders that affect the central nervous system, such as Guillain-Barré syndrome or multiple sclerosis
• Tumors located within the central nervous system (primary) or cancers that spread to the central nervous system (metastatic cancer)
• Alzheimer disease, an irreversible form of dementia

CSF testing usually involves an initial, basic set of tests performed when CSF analysis is requested:

• CSF color, clarity and pressure during CSF 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 the infection is suspected, CSF Gram stain, routine culture, and molecular tests that detect the genetic material of any microbes present

A wide variety of other tests may be ordered as follow-up depending on the results of the first set of tests or the suspected diagnosis. The specific tests that are ordered depending on your signs and symptoms and the disease your healthcare practitioner suspects may be the cause. Each of these tests can be grouped according to the type of exam that is performed. For more, see Details on CSF Tests below.