Rheumatoid arthritis is not a cause of a false-negative test for Lyme disease. And Lyme disease is not a known trigger of rheumatoid arthritis. In fact, there are no known triggers of rheumatoid arthritis. (The cause of the disease is unknown.)

Arthritis due to Lyme disease is diagnosed by a combination of symptoms, a physical exam, and antibody tests in a person exposed to the tick that transmits the disease. Helpful clues to the diagnosis of arthritis due to Lyme disease are:

• Finding an engorged tick attached to the skin followed by the start of joint symptoms
• A rash (called erythema migrans) that may have a "bull's eye" appearance days to weeks before joint symptoms start
• Pain and swelling in a joint, most commonly one knee
• Positive blood antibody results for Lyme disease

There are two common tests for Lyme disease. The first test is called an ELISA. The confirmatory test is called a Western Blot. A false-negative test means that the result is negative, or normal, despite having Lyme disease. This can happen if the test is done just after a tick bite or when the rash starts. This is because the immune system has not had a chance to create antibodies yet.

Having rheumatoid arthritis has no known effect on the accuracy of antibody tests for Lyme disease.

If the signs, symptoms, and antibody tests do not suggest that the person has arthritis due to Lyme disease, taking antibiotics against Lyme disease is unlikely to help.