The test is used to determine if your blood has made antibodies to the bacterium that causes Lyme disease. The infection affects many body systems, and in many patients starts with a “bulls-eye” rash at the site of the bite, and flu-like symptoms. The disease can progress and eventually cause a variety of chronic symptoms, including inflammation of the heart, arthritis, and central nervous system disease, including meningitis.

But because the symptoms of Lyme disease vary from person to person, and because antibodies to the bacterium do not appear until 3-6 weeks after the tick bite (although the skin lesion may appear within 3 to 30 days), the infection is difficult to diagnose. At this point, a blood test can be used to detect levels of antibodies, immunoglobulin M (IgM) and immunoglobulin G (IgG), that develop against the Borrelia burgdorferi bacterium.

This test, however, can also detect antibodies to other bacteria. Therefore, if the test is positive, an additional test, called a Western Blot, is often required to confirm the presence of specific antibodies to the bacterium that causes Lyme disease. Lastly, A DNA-based test based on the polymerase chain reaction (PCR) may also be done and is even more sensitive; it is used to detect the genetic material of the infecting bacteria. Taken together, these tests will help your doctor confirm a diagnosis. Once the diagnosis is made, your doctor will recommend appropriate treatment.

If you show the tell-tale sign of the tick bite and have recently been in an area with a large deer population, your doctor will probably diagnose you using these clinical findings. If you don’t have these clear signs but do have vague, confusing symptoms ranging from “flu,” numbness, and muscle and joint ache to arthritis, fatigue, and unexplained nerve or heart problems, your doctor may order these blood tests to see if you have Lyme disease.

A healthy adult has no antibodies to the Borrelia burgdorferi bacterium. If you test positive, you have been exposed to the bacterium and most likely have Lyme Disease. If you test negative, you could still have the disease, but your antibody level is too low to detect. In that case, your doctor will treat you according to your history and symptoms.

Antibodies to the bacteria can stay in the blood for a long time; therefore if you have ever been infected with Borrelia burgdorferi previously, your blood test might still be positive, even though you may no longer have Lyme disease.

Borrelia burgdorferi belongs to a class of bacteria called spirochetes. Other spirochete diseases (syphilis, leptospirosis) can cause false-positive results. Antibiotics can interfere with the test results, so if you are being treated with antibiotics before being tested for Lyme disease, make sure your doctor knows.