The main tests for Lyme disease and when they're used

Doctors use two main approaches to test for Lyme disease: blood tests that look for antibodies your immune system makes against the bacteria, and in some cases a test that directly detects the bacteria itself. The blood tests are far more common because they're reliable, widely available, and don't require specialized equipment. Most people with suspected Lyme disease will have blood drawn and sent to a lab—results typically come back within a few days to a week.

The timing of the test matters significantly. Early in infection (the first week or two), antibodies may not yet be present in measurable amounts, so a negative test doesn't rule out Lyme disease. This is why doctors often rely on symptoms and the history of a tick bite rather than waiting for test results before starting treatment. Later in infection, after the immune system has had time to respond, blood tests become much more reliable.

A small number of people with suspected Lyme disease may have a test called a Western blot, which is more detailed than standard screening tests. This test is usually ordered when an initial screening test is positive or when symptoms are unclear. It's also sometimes used to confirm diagnosis in people with late-stage Lyme disease affecting the joints or nervous system.

Key Takeaways

  • The standard test for Lyme disease is a blood test that detects antibodies, which takes several days to a week for results.
  • Early in infection (first one to two weeks), antibodies may not be present yet, so doctors often start treatment based on symptoms and tick exposure rather than waiting for test results.
  • A positive screening test is usually followed by a more detailed Western blot test to confirm the diagnosis.
  • Direct detection of the bacteria itself is rarely done outside research settings because it's technically difficult and slower than antibody testing.
  • Test results must be interpreted alongside your symptoms and medical history—a positive test alone doesn't always mean you have active Lyme disease.

How the two-step blood test process works

When you have blood drawn for Lyme disease, the lab typically performs a two-step process. First comes a screening test, usually an ELISA (enzyme-linked immunosorbent assay), which is fast and inexpensive. This test looks for antibodies to the Lyme bacteria in your blood. If this screening test is negative and your doctor has no strong reason to suspect Lyme disease, testing stops there.

If the screening test is positive or borderline, the lab then performs a Western blot as a confirmatory test. The Western blot is more specific—it looks at the exact pattern of antibodies and can distinguish Lyme disease from other infections that might trigger a false positive on the screening test. This two-step approach reduces the chance of misdiagnosis, because the screening test alone can occasionally be positive when you don't actually have Lyme disease.

The CDC recommends this two-step process as the standard for diagnosis. Some labs may skip the Western blot if the screening test is clearly negative, but if there's any uncertainty, your doctor will order the second test. Both tests measure antibodies, not the bacteria itself, so they're looking for evidence that your immune system has encountered the infection.

Why early testing can be misleading

One of the trickiest aspects of Lyme disease testing is the window period—the gap between when infection starts and when antibodies become detectable. In the first week or two after a tick bite, your immune system hasn't yet produced enough antibodies to show up on a blood test, even though the bacteria is actively multiplying in your body. A negative test during this window doesn't mean you don't have Lyme disease.

This is why doctors don't always wait for test results before treating suspected Lyme disease. If you have the characteristic rash (erythema migrans), fever, and a known tick bite in an area where Lyme disease is common, your doctor may start antibiotics immediately without waiting for blood work. Starting treatment early, before antibodies develop, is actually more effective than waiting for test confirmation.

After about two to three weeks of infection, antibodies become reliably detectable. At this point, blood tests are much more accurate. If you're being tested weeks after a possible exposure, a negative result is more meaningful than an early negative would be.

What different test results actually mean

A negative screening test in the first few weeks of illness doesn't rule out Lyme disease—it may simply mean antibodies haven't developed yet. If your symptoms and exposure history suggest Lyme disease, your doctor may treat you anyway. A negative test after three or more weeks of symptoms is more reliable, though it still doesn't completely rule out infection in rare cases.

A positive screening test means antibodies were found, but it doesn't automatically mean you have Lyme disease. Other infections, including some other tick-borne illnesses, can cause false positives. This is why the Western blot confirmation is important. A positive screening test followed by a positive Western blot is strong evidence of Lyme disease, though your doctor will still consider your symptoms and exposure history.

A positive Western blot after a positive screening test is considered diagnostic for Lyme disease. However, antibodies can persist for months or even years after successful treatment, so a positive test doesn't always mean you have active infection right now. Your doctor uses the test result along with your current symptoms to decide whether treatment is needed.

An indeterminate or borderline result on either test means the lab found some antibodies but not enough to be clearly positive or negative. Your doctor may order a repeat test in a week or two, as antibody levels rise over time, or may make a clinical decision based on your symptoms without waiting for retesting.

Testing for Lyme disease in different stages

Early Lyme disease, caught within the first few weeks, is usually diagnosed based on the characteristic rash and symptoms rather than blood tests. The rash (erythema migrans) often appears three to thirty days after a tick bite and expands outward in a bull's-eye pattern. If you have this rash plus symptoms like fever or joint pain, and you know you were bitten by a tick in a Lyme-endemic area, your doctor may diagnose and treat you without blood work.

Late Lyme disease, which develops weeks to months after infection, is more likely to be confirmed by blood tests because antibodies are now clearly present. If you have joint swelling (Lyme arthritis), neurological symptoms (Lyme neuroborreliosis), or heart problems weeks after a tick bite, blood tests are more reliable and are typically ordered. At this stage, a positive test is more straightforward to interpret.

Post-treatment Lyme disease syndrome—persistent symptoms after treatment—cannot be diagnosed by blood tests, because antibodies remain positive even after the infection is cured. If you have ongoing symptoms months after treatment, your doctor will focus on your current symptoms and may order other tests to look for different causes, rather than relying on Lyme serology.

Other tests and when they're used

In rare cases, doctors may test cerebrospinal fluid (the fluid around the brain and spinal cord) for Lyme bacteria or antibodies when Lyme neuroborreliosis is suspected. This requires a lumbar puncture (spinal tap) and is only done when neurological symptoms are severe or diagnosis is unclear. It's not a routine test for Lyme disease.

Direct detection of the bacteria through culture or PCR (polymerase chain reaction) is possible but rarely done in clinical practice. These tests are technically difficult, slow, and expensive compared to antibody testing. They're mainly used in research settings or when diagnosis is particularly uncertain. Most doctors rely on antibody tests because they're faster and more practical.

If you have symptoms that could be Lyme disease but also could be another condition, your doctor may order additional tests—such as tests for other tick-borne illnesses like babesiosis or anaplasmosis, which can be transmitted by the same tick. These tests help narrow down the diagnosis when symptoms overlap.

Frequently Asked Questions

Can I test positive for Lyme disease years after I was treated?

Yes. Antibodies to Lyme disease can remain detectable for months or years after successful treatment, so a positive blood test doesn't tell you whether the infection is current or past. Your doctor will look at your current symptoms and medical history to determine whether you need treatment, not just the test result.

What if my test is negative but I still have symptoms?

If your test was done early (within the first two weeks), a negative result doesn't rule out Lyme disease—antibodies may not have developed yet. Talk to your doctor about repeating the test in a week or two, or about starting treatment based on your symptoms and exposure history. If your test was done weeks later and is still negative, your doctor will consider other possible causes of your symptoms.

Do I need a test if I have the characteristic rash?

Not necessarily. The bull's-eye rash (erythema migrans) is considered diagnostic for Lyme disease on its own, and many doctors will start treatment based on the rash without waiting for blood work. However, some doctors order blood tests anyway for documentation or if the rash appearance is unclear.

Can Lyme disease tests be wrong?

Yes, both false positives and false negatives can occur. False positives are more common early in infection or with certain other infections. False negatives happen when testing is done too early, before antibodies develop. This is why doctors use test results along with your symptoms, medical history, and exposure to tick bites when making a diagnosis.

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

Standard screening tests usually return results within a few days to a week. If a Western blot confirmation is needed, add another few days to a week. Some labs are faster than others, and results may come back sooner if the lab is local to your doctor's office.