Lyme disease can be difficult to diagnose because many of its symptoms mimic those of other conditions. In addition, the only distinctive hallmark unique to Lyme disease, the erythema migrans rash, is absent or is unnoticed in up to one fourth of the people who become infected. Although a tick bite is an important clue for diagnosis, most patients cannot recall having been bitten recently by a tick. This is not surprising, because the tick is tiny and the bite painless.
When a patient with possible Lyme disease symptoms does not develop the distinctive rash, doctors will rely on a detailed medical history and a careful physical examination for essential clues to an alternative diagnosis. These clues include history of a tick bite, exposure to tick-infested areas, the onset and type of symptoms, and ruling out other diseases that might cause those symptoms.
Laboratory tests can be helpful, but not in the earliest stages of the disease. Although the actual bacteria for Lyme are difficult to isolate in the blood, blood tests can detect antibodies that the immune system makes to fight off the bacteria. There isn't one perfect way to test for Lyme antibodies, but there are a variety of screening tests.
These tests can't be relied upon during the first few weeks of infection (when the rash first appears) because a patient's immune system has not yet produced enough antibodies to be detected. Antibiotics given to treat a Lyme infection might also prevent antibodies from reaching detectable levels if the infection is still causing symptoms. Some tests can't distinguish Lyme disease antibodies from other disease antibodies, so a patient with a different condition could test positive for Lyme disease. A lack of standardization of antibody tests and poor quality control might also contribute to inaccuracies in test results.
Last reviewed on 10/03/2007
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