Blood-tests Explained


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This website is intended to assist with patient education and should not be used as a diagnostic, treatment or prescription service, forum or platform. Always consult your own healthcare practitioner for a more personalised and detailed opinion

CSF Analysis


At a Glance

Why Get Tested?

To diagnose a disease or condition affecting the central nervous system such as infection, bleeding within the brain or skull, cancer, or autoimmune disorder

When to Get Tested?

When your healthcare provider suspects that your symptoms are due to a condition or disease involving your central nervous system

Sample Required?

A sample of cerebrospinal fluid (CSF) collected by a health practitioner from the lower back using a procedure called a lumbar puncture or spinal tap

Test Preparation Needed?

You will be instructed to empty your bladder and bowels prior to sample collection. It will be necessary to lie still in a curled-up fetal position during the collection and to lie flat and still for a time period after the collection.

The Test Sample

What is being tested?

Cerebrospinal fluid (CSF) is a clear, watery liquid that flows around the brain and spinal cord, surrounding and protecting them. A CSF analysis is a group of tests that evaluate substances in CSF in order to diagnose conditions affecting the brain and spinal cord (central nervous system).

CSF 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. It is continually produced, circulated, and then absorbed into the blood. About 17 ounces (500 mL) are produced each day. This rate of production means that all of the CSF is replaced every few hours. Thumbnail diagram of the brain

A protective blood-brain barrier separates the brain from the bloodstream and regulates the distribution of substances between the blood and the CSF. It helps keep large molecules, toxins, and most blood cells away from the brain. Any condition that disrupts this protective barrier may result in a change in the normal level or type of constituents 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.

Though a sample of CSF may be more difficult to obtain than, for example, urine or blood, the results may reveal more directly the cause of central nervous system conditions.

  • Infections and inflammation in the meninges, the layers of tissue that surround the spinal cord and brain, can disrupt the blood-brain barrier and allow white blood cells (WBCs) and red blood cells (RBCs) and increased amounts of protein into the CSF. Meningitis, an infection in the meninges, and encephalitis, an infection in the brain, can also lead to the production of antibodies, which can be detected in the CSF.
  • Autoimmune diseases that affect the central nervous system, such as Guillain-Barré syndrome and multiple sclerosis, can also produce antibodies that can be found in the CSF.
  • Cancers such as leukemia can lead to an increase in white blood cells in the CSF and cancerous tumors can result in the presence of abnormal cells.
  • Alzheimer disease is an irreversible form of dementia. Measuring amyloid beta 42 (Aß42) and tau protein in CSF may help establish a diagnosis for this disease.

These changes from normal CSF constituents make the examination of cerebrospinal fluid valuable as a diagnostic tool.

For more on CSF tests, see the "How is it used?" section.

How is the sample collected for testing?

A sample of cerebrospinal fluid (CSF) is collected by a health practitioner from the lower back using a procedure called a lumbar puncture or spinal tap. Often, three or more separate tubes of CSF are collected, and multiple tests may be run on the different samples.

Is any test preparation needed to ensure the quality of the sample?

The person being tested should empty their bladder and bowels prior to the sample collection. It will be necessary to lie still in a curled-up fetal position during the collection and to lie flat and still for a time period after the collection.

The Test