Laboratory Studies

The current recommended approach is a two-tier strategy using a sensitive enzyme-linked immunosorbent assay (ELISA) and, if positive, Western blot. ELISA is associated with a high false-positive rate, so all positive results must be confirmed with a positive Western blot. Western blot can test for both immunoglobulin M (IgM) and IgG antibodies to B. burgdorferi. IgM antibodies typically appear within 1 to 2 weeks and IgG in 2 to 6 weeks, after onset of EM rash. Only one third of patients with a single lesion of EM are seropositive at diagnosis (Verdon and Sigal, 1997). The presence of EM is itself enough to make the clinical diagnosis, and testing is not required. Negative serology in a suspected case should be followed by acute- and convalescent-phase samples (2-4 weeks after initial sample). False-positive ELISA test results can occur in RA, juvenile rheumatoid arthritis (JRA), SLE, and infectious mononucleosis. Serologic testing after treatment is not helpful because seroreactivity persists long after successful treatment.

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