What doctors look for when checking for Lyme disease

Checking for Lyme disease starts with your doctor asking about a tick bite and a rash. The most reliable sign is an expanding red rash called erythema migrans, which often appears 3 to 30 days after a tick carrying the Borrelia burgdorferi bacteria bites you. The rash typically starts at the bite site and spreads outward, sometimes forming a "bull's-eye" pattern with a clear center, though many rashes do not have that shape.

If you have the characteristic rash and remember a tick bite in an area where Lyme disease is common, your doctor may start treatment without any blood test. This is because early treatment is most effective, and waiting for test results can delay care. If there is no rash or if the rash appeared weeks ago, your doctor will order blood tests to look for antibodies your body made in response to the infection.

The timing of your symptoms matters because antibodies take time to develop. Tests done within the first week of illness often come back negative even if you have Lyme disease, because your immune system has not yet produced detectable antibodies. This is why doctors rely on the rash and history of tick exposure in early cases.

Key Takeaways

  • An expanding red rash at the site of a tick bite, appearing 3 to 30 days after the bite, is the most reliable early sign of Lyme disease and often leads to treatment without waiting for blood tests.
  • Blood tests look for antibodies to Borrelia burgdorferi, but these antibodies may not show up until 1 to 2 weeks after symptoms start, making early rash recognition more useful than early testing.
  • A two-step testing process—an initial screening test followed by a confirmatory test if the first is positive—is the standard approach when blood tests are needed.
  • Symptoms beyond the rash, such as joint pain, fatigue, and neurological problems, develop over weeks to months and prompt testing when the rash is no longer visible.

Blood tests and how they work

When your doctor orders blood tests for Lyme disease, they typically use a two-step process. The first step is an enzyme immunoassay (EIA) or immunofluorescence assay (IFA), which screens for antibodies to the Lyme bacteria. If this test is positive or borderline, the second step is a Western blot, which confirms the result by checking for antibodies to specific proteins from the bacteria.

This two-step approach exists because the first screening test can sometimes be positive when you do not actually have Lyme disease—a false positive. The Western blot is more specific and catches these errors. The CDC recommends this exact sequence, and most labs follow it. If your screening test is negative, you typically do not need the Western blot unless your doctor has strong clinical reasons to suspect Lyme disease despite the negative result.

The timing of testing affects the results. During the first week of illness, antibodies may be too low to detect, so a negative test does not rule out Lyme disease if you have the characteristic rash. After 2 to 3 weeks, antibodies are usually detectable. If you were treated with antibiotics early, your antibody levels may stay lower or develop more slowly than in untreated cases.

When to get tested

You should see a doctor and discuss testing if you have an expanding rash after a tick bite, especially if the bite occurred in a region where Lyme disease is present. The northeastern United States, upper Midwest, and parts of the Pacific coast have the highest rates of Lyme disease. If you live in or visited one of these areas and developed a rash weeks after a tick bite, mention this to your doctor.

Testing also makes sense if you have symptoms that could be Lyme disease but no rash—such as joint pain, particularly in the knees; unexplained fatigue; or neurological symptoms like facial drooping or numbness. These symptoms can develop weeks or months after infection. Your doctor will ask about tick exposure and the timing of your symptoms to decide whether testing is warranted.

If you had a tick bite but no rash and feel fine, testing is not usually recommended. Most people bitten by ticks do not get Lyme disease, and testing without symptoms can produce false positives that lead to unnecessary treatment. The exception is if you develop symptoms later—then testing becomes relevant.

What a positive test means

A positive Lyme disease test means you have antibodies to the Borrelia burgdorferi bacteria, which indicates you were infected at some point. It does not tell you when the infection occurred or whether you still have active infection. Someone who was treated successfully months ago will still test positive because antibodies persist in the blood for years.

This is why your doctor will combine the test result with your symptoms and history. A positive test plus an expanding rash or recent symptoms of Lyme disease means you likely have active infection and need treatment. A positive test in someone with no symptoms and no history of Lyme disease symptoms may mean a past infection that resolved, or occasionally a false positive despite the two-step process.

If your test is positive and you have symptoms, your doctor will typically prescribe antibiotics. The choice of antibiotic and length of treatment depend on which stage of Lyme disease you have—early localized (rash only), early disseminated (rash plus systemic symptoms), or late (joint, neurological, or cardiac symptoms weeks to months later).

What a negative test means

A negative Lyme disease test means the screening test did not find antibodies to the bacteria. If you had the test done within the first week of symptoms, this does not rule out Lyme disease—your antibodies may not have developed yet. If you have the characteristic rash and a negative early test, your doctor will likely treat you anyway rather than wait for antibodies to appear.

If you had the test done 2 or more weeks after symptoms started and it is negative, Lyme disease is much less likely, though not impossible. Your doctor may repeat the test or order additional tests if they still suspect Lyme disease based on your symptoms and exposure history. In rare cases, people with Lyme disease do not develop detectable antibodies, or the infection is caught so early that antibodies have not formed.

A negative test does not mean you should ignore symptoms. If you have joint pain, fatigue, or neurological symptoms that persist after a tick bite, discuss this with your doctor even if the test is negative. They may consider other diagnoses or recommend a follow-up test.

Other tests your doctor might order

Beyond the standard two-step blood test, your doctor may order additional tests depending on your symptoms. If you have neurological symptoms like meningitis or facial nerve paralysis, a spinal tap (lumbar puncture) may be done to check for Lyme bacteria or antibodies in the cerebrospinal fluid. This test is more specific for Lyme disease of the nervous system than blood tests alone.

If you have joint pain and swelling, particularly in the knees, your doctor may order imaging such as X-rays or an MRI to rule out other causes. In some cases, they may perform a joint aspiration—removing fluid from the joint—to test for Lyme bacteria or antibodies. This is typically done only when the diagnosis is unclear or when symptoms are severe.

Some doctors order tests for co-infections transmitted by the same tick that carries Lyme disease, such as babesiosis or anaplasmosis. These tests are not routine but may be considered if you have symptoms that do not fit typical Lyme disease or if you live in an area where co-infections are common.

Symptoms that prompt testing

The expanding rash is the clearest sign, but other symptoms developing after a tick bite should prompt you to see a doctor. Early symptoms include fever, chills, fatigue, body aches, and headache—which can resemble flu. These typically appear within 3 to 30 days of the tick bite. If you remember a tick bite and develop these symptoms, tell your doctor about the tick exposure.

Later symptoms, appearing weeks to months after infection, include joint pain and swelling (most often in the knees), facial drooping on one or both sides (Lyme facial palsy), numbness or tingling in the hands or feet, and heart palpitations or chest pain. These delayed symptoms are less obviously connected to a tick bite, so mentioning your tick exposure history is important. Your doctor may not think to test for Lyme disease unless you bring up the tick bite.

Some people have no memory of a tick bite or rash but develop these later symptoms. If you live in or visited a Lyme disease area and have unexplained joint pain or neurological symptoms, mention this to your doctor. They can decide whether Lyme disease testing is appropriate based on your full history.

Frequently Asked Questions

Can I test for Lyme disease at home?

Home test kits exist but are not recommended by the CDC or major medical organizations. They are less reliable than laboratory tests performed by trained technicians using standardized methods. If you think you may have Lyme disease, a test ordered by your doctor through a certified laboratory is more trustworthy.

How long does it take to get Lyme disease test results?

Results typically come back within 3 to 7 business days, though this varies by laboratory and whether a confirmatory Western blot is needed. Some urgent care or hospital labs may have faster turnaround. Ask your doctor's office how long to expect.

If I was treated for Lyme disease, will I test positive forever?

Yes, antibodies to Lyme disease bacteria persist for years after successful treatment. A positive test does not mean you still have active infection. Your doctor will look at your current symptoms and history to determine whether a positive test reflects past or present infection.

What should I do if I find a tick on my skin?

Remove it promptly with tweezers, grasping it close to the skin and pulling straight out. Do not squeeze the tick or use heat or oil. Wash the area with soap and water. Save the tick in a sealed bag if possible—some labs can test ticks for Lyme disease bacteria, though this is not routine. Watch for a rash over the next month and see a doctor if one appears.

Can Lyme disease be prevented after a tick bite?

A single dose of the antibiotic doxycycline taken within 72 hours of a tick bite may prevent Lyme disease in some cases, though this is not standard practice for all tick bites. Talk to your doctor if you remember a tick bite and are concerned about infection. They can assess your risk based on the tick type, how long it was attached, and your location.