The two-step blood test is the standard, but timing matters more than which test you choose

The most accurate way to detect Lyme disease is a two-step blood test: an initial screening called an ELISA (enzyme-linked immunosorbent assay), followed by a confirmatory test called a Western blot if the first test is positive. This combination catches most cases of Lyme disease while keeping false positives low. However, the test's accuracy depends heavily on when you take it—a test done too early in infection may miss the disease entirely, even though it is the right test.

No single test is perfect for Lyme disease at all stages. The bacteria that causes Lyme disease, Borrelia burgdorferi, takes time to spread through the body and trigger an immune response that blood tests can detect. This timing problem means that a negative test early in illness does not rule out Lyme disease, and some people with late-stage Lyme disease may test negative even with the two-step approach.

Key Takeaways

  • The two-step test (ELISA followed by Western blot) is the standard recommended by the CDC and catches most cases of Lyme disease when done at the right time.
  • Tests done within the first week of a tick bite often come back negative even in people who have Lyme disease, because antibodies have not yet developed.
  • A positive ELISA alone is not considered confirmed Lyme disease—the Western blot must also be positive to meet the CDC case definition.
  • Some people with late-stage Lyme disease, particularly those with neurological symptoms, may test negative on standard blood tests and may need additional testing.

How the two-step test works and why it is the standard

The ELISA test detects antibodies your immune system makes against the Lyme bacteria. It is fast, inexpensive, and catches most people with Lyme disease—but it also produces false positives more often than doctors want. That is why the CDC recommends that any positive ELISA be confirmed with a Western blot, which is more specific and looks for antibodies against individual proteins from the bacteria.

Together, these two tests form what the CDC calls the "two-tier" approach. A person is considered to have confirmed Lyme disease only if the ELISA is positive and the Western blot is positive. This combination reduces the chance of a false positive from roughly 1 in 20 with ELISA alone to less than 1 in 1,000 with both tests together. Most labs in the United States follow this standard, and most insurance plans cover both tests when ordered by a doctor.

Why timing changes what the test can find

The Lyme bacteria does not trigger a detectable antibody response immediately. In the first week after infection, your immune system is still ramping up, and blood tests often come back negative even though you have the disease. By the second or third week, most people with Lyme disease will test positive on the two-step test. By several months in, nearly all people with untreated Lyme disease will test positive.

This timing problem means that if you were bitten by a tick and develop symptoms within days, a negative test does not mean you do not have Lyme disease. Your doctor may recommend starting treatment based on symptoms and exposure history alone, without waiting for test confirmation. Once you have had Lyme disease, your antibodies remain detectable for years, even after successful treatment, so a positive test does not tell you whether the infection is current or past.

What happens if the ELISA is positive but the Western blot is negative

A positive ELISA with a negative Western blot is called a discordant result, and it does not meet the CDC definition of confirmed Lyme disease. This pattern occurs in roughly 5 to 10 percent of people tested and is usually a false positive on the ELISA—the initial test picked up antibodies from a different infection or a cross-reacting condition.

If you have this result and your symptoms fit Lyme disease, your doctor may order the tests again in a few weeks, since antibodies can take time to develop fully. Some doctors may also consider your clinical symptoms, your history of tick exposure, and whether you have the characteristic rash of early Lyme disease (erythema migrans). A rash that expands outward from the bite site is strong evidence of Lyme disease on its own and may prompt treatment even with discordant blood tests.

Other tests that may be used when standard tests are unclear

When the two-step test is negative but Lyme disease is still suspected—particularly in people with neurological symptoms like meningitis or facial nerve paralysis—doctors sometimes order a test on cerebrospinal fluid (CSF) instead of blood. The CSF is collected by lumbar puncture and tested for Lyme antibodies. This test is more specific for Lyme disease of the nervous system and can catch cases that blood tests miss.

Some laboratories offer additional tests like the C6 peptide ELISA, which targets a specific part of the Lyme bacteria and may be slightly more specific than the standard ELISA. However, the C6 test is not yet part of the CDC-recommended two-tier approach and is not routinely covered by insurance. It may be ordered by specialists in areas where Lyme disease is common or when standard tests give unclear results.

Why you should not rely on tests ordered outside a doctor's office

Some commercial laboratories and direct-to-consumer testing companies offer Lyme disease tests without a doctor's order, and some use non-standard methods that are not validated by the CDC. These tests may have higher false positive rates or may not follow the two-tier approach. If you order a test this way and it comes back positive, you should still see a doctor who can order the standard two-step test and evaluate your symptoms before starting treatment.

Similarly, some alternative medicine practitioners offer tests they claim are more sensitive than standard blood tests—such as darkfield microscopy or specialized culture methods. These tests are not supported by evidence and are not recommended by the CDC or infectious disease specialists. If you have been tested by these methods, a standard two-step test ordered by your doctor remains the most reliable way to know whether you have Lyme disease.

What to expect after a positive test

A positive two-step test means you have been infected with the Lyme bacteria at some point. Your doctor will then determine whether you need treatment based on your symptoms, how long ago you were infected, and what stage of disease you have. Early Lyme disease (within the first month) is treated with oral antibiotics. Later-stage disease, particularly Lyme arthritis or neurological Lyme disease, may require intravenous antibiotics or longer courses of oral treatment.

After treatment, your antibodies will remain positive for months or years, so a repeat test will not tell you whether the infection has been cured. Your doctor will assess cure based on whether your symptoms improve. Some people have persistent symptoms after treatment (called post-treatment Lyme disease syndrome), but this is not the same as active infection and does not require additional antibiotics.

Frequently Asked Questions

Can I test positive for Lyme disease if I was never bitten by a tick?

Yes, though it is uncommon. You could have been bitten without noticing, or the tick could have been very small. You could also have a false positive ELISA result, which is why the Western blot confirmation is important. If you test positive but have no history of tick exposure and no symptoms of Lyme disease, your doctor may repeat the test or order additional testing before starting treatment.

How long after a tick bite should I wait to get tested?

Wait at least one to two weeks after the bite or after symptoms start. Testing too early will often give a false negative. If you develop symptoms suggestive of Lyme disease (rash, fever, joint pain) within days of a tick bite in an area where Lyme disease is common, your doctor may recommend treatment without waiting for test results.

If I test negative, can I still have Lyme disease?

Yes, particularly if you were tested very early in infection (within the first week). A negative test does not rule out Lyme disease if you have symptoms and a history of tick exposure. Your doctor may recommend treatment based on clinical findings alone, or may repeat the test in one to two weeks when antibodies are more likely to be detectable.

Does a positive Lyme test mean I need treatment right now?

Not necessarily. A positive test means you have been infected, but your doctor needs to know whether the infection is current and what stage it is in. If you were treated for Lyme disease months or years ago, you will still test positive. Your doctor will use your symptoms and the timing of your illness to decide whether treatment is needed.

What is the difference between the ELISA and the Western blot?

The ELISA is a screening test that detects antibodies against the whole Lyme bacteria—it is sensitive but not very specific, meaning it catches most cases but also produces some false positives. The Western blot is a confirmation test that looks for antibodies against individual bacterial proteins—it is more specific and rules out most false positives. Together they form the standard two-step test.