Antibody Blood Test: What It Is and Why It Is Done

An antibody blood test measures proteins your immune system makes to fight germs or, in some cases, your own healthy tissue. Your provider may order this test to look for a current or past infection, to help diagnose an autoimmune condition, or to check how your body responded to a vaccine. The results help guide diagnosis and treatment decisions.

This test measures three types of antibodies (IgM, IgG, and IgA) against Borrelia burgdorferi, the bacteria that causes Lyme disease, in your cerebrospinal fluid (CSF). CSF is the clear fluid that surrounds your brain and spinal cord. The test helps doctors determine if Lyme disease has spread to your nervous system, a condition called neuroborreliosis.

Most antibody tests are done with a blood sample drawn from a vein in your arm, usually on the inside of the elbow. A clinician cleans the site, wraps a band around your upper arm, and collects the sample into a small tube. The draw takes only a few minutes, and you can return to your normal activities right afterward.

CSF is collected through a procedure called lumbar puncture (spinal tap). A healthcare provider inserts a thin needle into the lower back to draw a small amount of fluid from the space around the spinal cord. The procedure takes about 15-30 minutes, and you may need to lie flat for a short time afterward.

Different antibodies point to different things. IgM antibodies usually appear first and may suggest a recent or current infection, while IgG antibodies often develop later and can stay in your blood for years, showing past exposure or lasting protection. Antibodies that attack your own tissues may signal an autoimmune disease, so your provider interprets each result together with your symptoms and history.

IgM antibodies usually appear first (within 1-2 weeks of infection) and indicate early infection. IgG antibodies develop later (2-4 weeks after infection) and show a later or ongoing infection. IgA antibodies are also measured in CSF and can provide additional diagnostic information. Detecting these antibodies specifically in CSF (rather than blood) suggests the immune system is producing antibodies locally in the central nervous system.

During the test, you will sit in a chair while a phlebotomist ties a band around your arm and asks you to make a fist. A needle is inserted briefly to draw blood, and you may feel a quick pinch. After the sample is collected, pressure and a bandage are applied to the site, and your blood is sent to a laboratory for analysis.

After the CSF sample is collected, it is sent to a laboratory where technicians test it for the presence and levels of IgM, IgG, and IgA antibodies against Borrelia burgdorferi. Results are typically available within a few days to a week, depending on the laboratory.