Lyme Disease Test
A Lyme disease test detects antibodies to the Lyme disease bacteria Borrelia burgdorferi in the blood. Lyme disease can be difficult to diagnose properly because its symptoms are similar to those of many other diseases.
When making a diagnosis of Lyme disease, health care practitioners should consider other diseases that may cause similar symptoms. Not all patients with Lyme disease will develop the characteristic bulls-eye rash, and many may not even recall a recent tick bite.
Lyme disease testing is not recommended for individuals who do not have symptoms of Lyme disease. Validated laboratory tests can be very helpful but are not normally recommended when a patient has erythema migrans (bull’s-eye rash).
Several forms of laboratory testing for Lyme disease are available, some of which have not been adequately validated. Most recommended tests are blood tests that measure antibodies made in response to the infection. These tests may be falsely negative in patients with early disease, but they are quite reliable for diagnosing later stages of disease.
A blood test can be done to check for antibodies to the bacteria that cause Lyme disease. The most frequent one used is the ELISA for Lyme disease test. A Western blot test is done to substantiate ELISA results. A skin biopsy can sometimes discover the Lyme disease bacteria as well.
CDC recommends a two-step process when testing blood for evidence of Lyme disease. Both steps can be done using the same blood sample.
1) The first step uses an ELISA or IFA test. These tests are designed to be rapid and very “sensitive,” meaning that almost everyone with Lyme disease, and some people who don’t have Lyme disease, will test positive. If the ELISA or IFA is negative, it is highly unlikely that the person has Lyme disease, and no further testing is recommended. If the ELISA or IFA is positive or indeterminate (sometimes called “equivocal”), a second step should be performed to substantiate the results.
2) The second step uses a Western blot test. Used properly, this test is designed to be “specific,” meaning that it will generally be positive only if an individual has been in fact infected. If the Western blot is negative, it suggests that the first test was a false positive, which can occur for a number of reasons. Occasionally two types of Western blot are performed, “IgM” and “IgG.”
Patients who are positive by IgM but not IgG should have the test repeated a few weeks later if they stay ill. If they are still positive only by IgM and have been ill longer than one month, this is likely a false positive. The Western blot test is often done to detect a chronic Lyme disease infection.
The CDC does not advocate testing blood by Western blot without first testing it by ELISA or IFA. Doing so increases the potential for false positive results. Such results may lead to patients being treated for Lyme disease when they don’t have it and not getting suitable treatment for the true cause of their ill health.
The tests are usually not positive in the first few weeks after the initial tick bite. They are frequently not accurate early in the infection. Timely treatment with antibiotics may prevent this test from ever being positive.
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