Understanding Your Laboratory Blood Test: A Patient Guide to Testing, Sample Collection, and Interpreting Your Results

This test is a laboratory analysis, most often performed on a sample of your blood, that helps your healthcare provider evaluate how well your body is functioning and look for signs of illness, infection, or other health conditions.

This test looks for IgG antibodies against Borrelia burgdorferi, the bacterium that causes Lyme disease, in the synovial fluid (joint fluid). IgG antibodies are produced by the immune system several weeks after infection and remain in the body for a long time, providing long-term immunity.

Your doctor may order this test to confirm or rule out a suspected condition, monitor an ongoing health problem, screen for disease before symptoms appear, or check how well a current treatment plan is working over time.

This test is primarily ordered when a patient has symptoms of Lyme disease arthritis, such as joint pain, swelling, and stiffness—particularly in the knees, though other joints may be affected. It helps doctors confirm whether the joint symptoms are caused by a Borrelia burgdorferi infection. The test is especially useful when initial blood tests for Lyme disease are inconclusive or when the infection has spread to the joints.

A trained healthcare professional will typically draw a small amount of blood from a vein in your arm using a sterile needle, although some tests may require a urine or swab sample, and the collection process usually takes only a few minutes.

A healthcare provider will collect a sample of synovial fluid from the affected joint using a needle and syringe in a procedure called arthrocentesis. This procedure is typically performed in a clinic or hospital setting. The area will be cleaned and numbed to minimize discomfort. After the fluid is collected, it is sent to a laboratory for analysis.

Your results will be compared against established reference ranges, and values that fall outside these ranges may point to an infection, a nutritional deficiency, a chronic condition, or simply the need for follow-up testing with your provider.

A positive result indicates that IgG antibodies to Borrelia burgdorferi were detected in the joint fluid, suggesting that the patient has or had a Lyme disease infection that has affected the joint. A negative result means no antibodies were detected, but this does not completely rule out Lyme disease, especially in early stages of infection or if the patient has been recently infected.

This test is very safe, but you may experience minor bruising, slight soreness, or brief dizziness at the needle site, and serious complications such as infection or excessive bleeding are extremely rare.

The main risks associated with sample collection include minor bleeding, infection, or bruising at the puncture site. Some patients may experience temporary discomfort or swelling in the joint after the procedure. These risks are generally minor and resolve quickly.