The standard test for Lyme disease is a two-step blood test that looks for antibodies your immune system produces in response to the bacteria. Both steps are required, and they can be run from a single blood draw. Results typically take one to two weeks.
How the Two-Step Test Works
The CDC recommends a two-tier testing process. The first step is a screening blood test called an enzyme immunoassay (EIA), which checks whether your blood contains antibodies against the Lyme bacteria. If this first test comes back negative, testing stops there. No further testing is needed.
If the first test is positive or borderline, a second test is run to confirm the result. In the traditional approach, this second step is a Western blot, which looks for antibodies reacting to specific proteins from the Lyme bacteria. The overall result is only considered positive when both the first and second tests are positive. This two-step design exists because the first screening test can sometimes react to things other than Lyme, and the confirmatory test filters out those false alarms.
Increasingly, labs are using a newer approach called modified two-tier testing, which replaces the Western blot with a second, different EIA. Both tests must be FDA-cleared to work together. The interpretation logic is the same: both tiers need to be positive for a positive result.
Why Timing Matters
These tests don’t detect the bacteria itself. They detect your body’s immune response to it, which takes time to build. In the first seven days after a tick bite, antibody levels are too low for any current blood test to pick up. The early-response antibodies (IgM) typically peak between 8 and 14 days after tick contact. The longer-lasting antibodies (IgG) follow in two to four weeks.
This means if you’re tested too early, you can get a negative result even though you’re infected. If your doctor suspects a very recent infection and your test comes back negative, the standard recommendation is to retest with a new blood sample in 7 to 14 days.
There’s also a timing rule on the other end. The early-response IgM antibodies are only considered meaningful if your symptoms started within the past 30 days. After that window, IgM results become unreliable because they can stay elevated long after the infection has cleared, or they can produce false positives. For anyone with symptoms lasting more than 30 days, only the IgG results matter.
What a Positive Result Tells You
A positive two-tier test confirms that your body has produced antibodies against the Lyme bacteria at some point. It doesn’t tell you exactly when the infection happened. Antibodies can remain detectable for months to years after successful treatment, so a positive result doesn’t necessarily mean you have an active infection right now. Your doctor interprets the result alongside your symptoms, exposure history, and where you live or have traveled.
A positive result also can’t be used to track whether treatment is working. Antibody levels don’t drop in a predictable way after antibiotics, so retesting to confirm you’re “cured” isn’t useful.
What About Testing Without Symptoms?
If you’ve been bitten by a tick but feel fine, testing isn’t recommended. The 2020 guidelines from the Infectious Diseases Society of America, the American Academy of Neurology, and the American College of Rheumatology specifically advise against testing asymptomatic people after tick bites. Without symptoms, a positive antibody test creates more confusion than clarity, since it could reflect a past exposure that never caused illness.
For the same reason, testing the tick itself for Lyme bacteria is also discouraged. Whether or not the tick carries the bacteria doesn’t reliably predict whether you’ll develop an infection. Having the tick identified to species is useful, though, since only certain tick species transmit Lyme.
When PCR Testing Is Used
In certain situations, doctors use a different kind of test that detects the bacteria’s DNA directly rather than looking for antibodies. This is called PCR testing, and it’s not a first-line tool. It plays a supporting role in specific scenarios.
PCR is most useful when testing joint fluid in suspected Lyme arthritis, where it can detect bacterial DNA in the synovial fluid or tissue. It also has value for testing skin biopsies when a rash doesn’t look like the classic bull’s-eye pattern and needs confirmation. PCR can sometimes detect Lyme DNA in spinal fluid, but this is less reliable and is only recommended for patients who already have a positive blood antibody test along with abnormal spinal fluid findings. In all cases, PCR results are interpreted alongside standard antibody testing, not as a standalone answer.
Getting Tested
Lyme testing requires a standard blood draw, typically ordered by your primary care doctor. The blood is sent to a lab, and results come back in one to two weeks depending on the lab and which testing method is used. The modified two-tier approach using two EIAs can be faster than the traditional Western blot route, since it’s more easily automated.
One important thing to keep in mind: the characteristic bull’s-eye rash that appears in many Lyme cases is considered diagnostic on its own in areas where Lyme is common. If you have that rash and a recent tick exposure, your doctor may start treatment without waiting for blood test results, since testing in the first week or two of infection often produces a false negative anyway.