Positive Lyme Test Results: What Do They Mean and What Happens Next?

Positive Lyme test results mean that antibodies to Borrelia burgdorferi, the bacteria that cause Lyme disease, were found in your blood. MedlinePlus notes that a positive result does not confirm Lyme disease by itself: the test can also pick up a past infection or react to other conditions. Your clinician reads the result together with your symptoms, how long you have had them and whether you could have been bitten by a tick.

This guide is for adults with a reported Lyme blood test. It explains how the testing works and the questions worth asking. It cannot tell you whether you have Lyme disease or whether you need treatment.

NHS advises asking for an urgent GP appointment, or contacting a local urgent advice service, if you have been bitten by a tick or visited an area with ticks in the past 3 months and have flu-like symptoms or a round or oval rash. CDC lists later problems that can appear days to months after a bite. Seek prompt medical care if you notice:

• Drooping or weakness on one or both sides of the face (facial palsy).
• Heart palpitations or an irregular heartbeat. Fainting, chest pain or severe breathlessness need emergency care.
• Severe headache with neck stiffness.
• Severe joint pain and swelling, especially in the knee or another large joint.
• Nerve pain, numbness or tingling in the hands or feet.

CDC recommends a two-step antibody process using tests cleared by the US Food and Drug Administration. Both steps are needed, and they can be run on the same blood sample. If the first step is negative, no further testing is recommended.

In standard two-tier testing, a first immunoassay (often called an EIA or ELISA) is followed by a western blot, also called an immunoblot. In modified two-tier testing, which more laboratories now use, two different immunoassays are used instead of a blot. A result counts as positive only when both steps are positive or equivocal. A positive first step alone is not a positive Lyme test.

Guidance outside the US is similar in principle. NHS describes two types of blood test that can help confirm or rule out Lyme disease, and notes that they are not always accurate early in the illness. Check your report to see which tests were done and whether both steps were completed.

Lyme tests can report two kinds of antibody. Laboratory guidance prepared with CDC explains that the body makes IgM antibodies first and the longer-lasting IgG antibodies later. IgM tests can pick up infection earlier, but they are less specific and more likely to give false positive results.

Timing matters. CDC states that positive IgM results should be disregarded if the person has been ill for more than 30 days. By then, someone with untreated Lyme disease would usually have IgG antibodies. A positive IgG result is consistent with infection in the recent or remote past, so it cannot show when the infection happened. Some newer tests detect both types together and do not separate them.

Yes. CDC lists cross-reactions with relapsing fever, syphilis, rheumatoid arthritis and Epstein-Barr virus infection. MedlinePlus adds that some autoimmune diseases can cause a positive result, and that these may be the real cause of the symptoms.

False positives are more likely when the chance of Lyme disease was low to begin with, such as when there was no likely exposure to ticks in an area where Lyme disease occurs. Results are also less reliable when only one step is done, when an immunoblot is run without a positive first test, or when a laboratory uses tests that are not FDA-cleared or its own interpretation criteria. The CDC-supported guidance advises against these approaches.

A positive result without symptoms is most often explained by antibodies from a past infection or a false positive. CDC explains that once your blood tests positive, it will likely stay positive for months to years, even after the bacteria are gone. This does not mean the infection is still active, and having antibodies does not reliably protect you from catching Lyme disease again.

The Infectious Diseases Society of America and partner societies recommend against testing people without symptoms after a tick bite. Antibody tests also should not be used to check whether treatment worked; response to treatment is judged by how symptoms settle. If you had a positive result without symptoms, ask your clinician whether treatment is needed rather than assuming either way.

Often not. The typical rash, erythema migrans, starts at the bite site 3 to 30 days after the bite, with an average of about 7 days, according to CDC, and NHS notes it can appear up to 3 months later. It spreads gradually, may look like a bullseye, and can be harder to see on brown or black skin.

Guidance from IDSA and laboratory guidance prepared with CDC say that a clinician can diagnose Lyme disease from a typical rash in someone who lives in or has travelled to an area where Lyme disease occurs, without a blood test. Testing at this stage is often unhelpful because antibodies may not have formed yet. CDC notes tests may be falsely negative in the first 4 to 6 weeks.

Bring the full laboratory report and a note of when symptoms started and any possible tick exposure, including travel. These questions can help:

• Were both steps of two-tier testing done, and was it the standard or modified method?
• Was the positive result IgM, IgG or both, and how does that fit with how long I have had symptoms?
• Do my symptoms and possible tick exposure fit Lyme disease, or could something else explain the result?
• Could an earlier infection, or a condition such as an autoimmune disease or a recent viral illness, have caused a positive result?
• Is treatment recommended, and how will we judge whether it has worked?
• Which new symptoms should make me seek care sooner?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with a similar test pattern, timing and exposure history described their situation, and which questions they took to their clinician, can help you prepare for your own appointment. Similar cases cannot interpret your result, and we do not offer a diagnosis or treatment advice.