The testing for Lyme disease usually involves an initial ELISA test that if positive requires a confirmatory Western Blot test. It must be recognized, however, that these tests are limited in sensitivity and specificity and a diagnosis of Lyme disease requires integration of exposure risk, clinical findings, and serological test results. Reliance on testing alone will result in many incorrect diagnoses, both false positive and negative.

Clearly a patient who has been in a Lyme disease endemic area and who presents with the typical bulls-eye-shaped erythema migrans rash almost certainly has early Lyme disease. They should be treated irrespective of test results as testing will frequently be falsely negative in this situation. On the other hand, positive tests occurring in patients who lack significant epidemiologic exposure, or who are asymptomatic or have symptoms and signs not consistent with Lyme disease, probably represent false positive tests.

It’s imperative that an experienced, certified reference lab such as the National Microbiology Laboratory in Winnipeg performs the confirmatory testing. Unfortunately, many dubious, for-profit laboratories that don’t follow strict quality control and interpretation guidelines exist. I would not accept results from such labs.

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