The purpose of the most common type of Lyme disease testing is to determine whether you have developed antibodies as a result of past exposure to the Borrelia bacteria that cause Lyme disease. Antibodies are proteins created by the immune system that target specific threats like bacteria and viruses.
Blood testing alone cannot determine whether you have Lyme disease. Instead, testing can provide helpful information that your doctor can consider along with other factors, such as any symptoms you’ve had and whether you’ve been exposed to ticks that can carry Borrelia, to determine if a diagnosis of Lyme disease is appropriate.
Beyond blood testing, it is possible to analyze fluid from the central nervous system for signs of the Borrelia bacteria.
Who should get testing?
Testing is usually indicated if a person has symptoms of Lyme disease and a known or possible exposure to ticks that can carry the Borrelia bacteria. However, because it takes time for antibodies to develop, the timing of testing is important to consider.
Lyme disease symptoms depend on the extent of the bacterial infection. Three phases are used to describe the infection:
- Early localized: In this initial phase, symptoms are normally found only near the tick bite. This early stage is called erythema migrans and involves a noticeable rash that typically develops within a few weeks after being bitten.
- Early disseminated: In this phase, the bacteria move through the blood to affect other parts of the body and can cause general symptoms like fever, headaches, and pain. In some cases, the bacteria can affect the heart or nervous system.
- Late disease: This phase occurs long after the initial tick bite and most often includes symptoms affecting the joints or nervous system.
It is important to understand these phases because testing is not equally valuable in each stage. With early localized disease and erythema migrans, blood testing is generally not helpful because antibodies have not had enough time to develop.
In people with symptoms of early disseminated or late disease, testing can help determine whether they have had a previous Borrelia infection. Blood testing alone, though, does not diagnose Lyme disease. It is one factor to be considered alongside symptoms and potential tick exposure.
Some symptoms of Lyme disease, like joint pain, can be caused by many other health conditions. For this reason, testing is not recommended if you only have these kinds of nonspecific symptoms and no other indications of Borrelia exposure. In these cases, a positive test can be misleading because antibodies could be the result of a past infection rather than an active condition causing your present symptoms.
Because of similar concerns about potential false positive results, random screening for Lyme disease in people without symptoms is not recommended even in areas that are known to have ticks that can carry the Borrelia bacteria.
Testing of the cerebrospinal fluid is most often indicated when a person has neurological symptoms consistent with Lyme disease and positive or inconclusive blood tests.
Getting test results
For a blood test or lumbar puncture, you will likely receive test results from your doctor. Your doctor may call you with results or schedule you for a follow-up office visit. Results may also be sent to you through an online health portal or in the mail.
For at-home blood tests that are sent to a lab, you usually get results a few business days after your sample is received. Results are often provided through a smartphone app or website.
Lyme disease tests are generally effective for determining whether someone has been exposed to Borrelia, but, like any medical test, they are not perfect. There are considerations that can affect the accuracy of tests and how they are interpreted.
- Cross-reactivity: It is possible for antibodies to other bacteria to be detected by tests for antibodies to Borrelia. This is known as a false positive because the test shows Borrelia exposure when none actually occurred. A misleading positive result can also occur in patients who have previously had Lyme disease or who have received a vaccine for Lyme disease.
- Standardization of interpretation: The CDC has issued guidelines for how to interpret antibody test results. Studies have found that laboratories that follow these guidelines produce more consistent and reliable analyses than laboratories that apply non-standard criteria.
- Test timing: When the test is taken is important to consider because of the time it can take for different antibodies to develop and be detectable in the blood.
The laboratory and doctor can take these factors into account when interpreting your test results. Overall, testing is typically reliable in assessing bacteria exposure, but it is important to remember that this is distinct from a definitive diagnosis of Lyme disease.