Cerebrospinal Fluid (CSF) Analysis: What This Test Measures and Why It Matters

This test examines your cerebrospinal fluid (CSF), the clear liquid that surrounds and protects your brain and spinal cord. Doctors use it to help diagnose infections, bleeding, inflammation, and other conditions affecting the central nervous system.

This test detects IgG (immunoglobulin G) antibodies in your blood and cerebrospinal fluid against three species of Borrelia bacteria: Borrelia burgdorferi, Borrelia afzelii, and Borrelia garinii. These bacteria are transmitted through tick bites and cause Lyme disease, which is the most common tick-borne disease in many parts of the world.

Your CSF sample is sent to a laboratory, where specialists measure its pressure, protein, and glucose levels, count its cells, and examine it under a microscope for bacteria, viruses, or abnormal cells that may point to a specific condition.

When your body is exposed to Borrelia bacteria, your immune system produces specific antibodies to fight the infection. IgG antibodies typically appear 2-4 weeks after initial infection and remain in the body for a long time. This test uses an immunoassay technique to detect these antibodies in your serum (blood) and CSF (cerebrospinal fluid), which can indicate whether you have been infected with Lyme disease bacteria.

CSF testing is included because this fluid is in direct contact with your brain and spinal cord, so changes in its color, pressure, or chemistry can reveal meningitis, encephalitis, multiple sclerosis, or bleeding around the brain earlier than many other tests.

Testing cerebrospinal fluid is important when neurological symptoms of Lyme disease are suspected, such as meningitis, facial palsy, or nerve inflammation. The CSF test helps determine if the infection has spread to the central nervous system.

The sample is usually collected through a lumbar puncture, also called a spinal tap. After numbing your lower back with a local anesthetic, a thin needle is carefully inserted between two vertebrae to withdraw a small amount of fluid for testing.

For serum testing, a healthcare professional will draw blood from a vein in your arm. For CSF testing, a procedure called a lumbar puncture (spinal tap) is performed to collect cerebrospinal fluid from the lower back. Both samples are then analyzed in a laboratory using immunoassay techniques.