Understanding Cross Reactivity
Our immune system is pretty amazing - it keeps us healthy and prevents us from getting sick from the many different infection causing bacteria and viruses we come in contact with daily. However, our immune system is not perfect. While antibodies are quite specific and unique, they can make mistakes. Antibodies can be similar enough that it makes it difficult to tell the subtle differences between them, which is something we see in people with autoimmune diseases. People with autoimmune diseases can cause a specific antibody test to be measured as positive when it should be negative.
With all antibody tests, there can be cross reactivity between different infections that can cause results to be detected as positive when they should not be positive. For Lyme Disease, there are a few other infections that someone can have at the time of taking their lab test that may make their Lyme test result positive despite the person not being infected with Borrelia. When this happens, your Lyme test result is considered a “false positive” result.
What can cause a false positive Lyme test result? The two most common infections that can cause your Lyme titers to be positive are Epstein-Barr Virus (the virus that causes mononucleosis) and Toxoplasma gondii (a parasitic infection). Less commonly, individuals with Syphilis and Parvovirus B19 (also known as Fifth’s Disease) can have positive Lyme disease titers.
It is important to remember that a diagnosis of Lyme disease cannot be made on lab test results alone. Exposure to infected blacklegged ticks and symptoms consistent with Lyme disease infection should also be present to have a diagnosis of Lyme made by a healthcare professional. A Lyme disease lab test result can help guide your discussion with a healthcare professional, but only a healthcare professional can positively diagnose this condition.