Significance of Isolated Positive IgM Serologic Results by Enzyme Immunoassay for Coccidioidomycosis.
Blair, Janis E. 1; Currier, Jeremiah T. 2
[Article] Mycopathologia. 166(2):77-82, August 2008.

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Serologic testing is important for diagnosis of coccidioidomycosis. Many methods are available for diagnostic testing. Enzyme immunoassay (EIA) can be performed quickly and locally but has the potential for false-positive results in patients manifesting a positive EIA for immunoglobulin M (IgM) antibodies and a negative EIA for immunoglobulin G (IgG). We retrospectively reviewed the charts of 405 patients with coccidioidal serologic testing performed between 1999 and 2003. Of 706 EIAs, 37 (5%) produced test results for 28 patients that showed isolated IgM positivity. Among these 28 patients, 24 (86%) had positive serologic findings by other methods (complement fixation or immunodiffusion or both), and 7 (25%) had positive microbiologic or histopathologic findings. All 4 (14%) patients without other positive serologic results had diagnostic tests with positive microbiologic or histopathologic results. No false-positive IgM assays were observed. We conclude that the false-positive rate of the EIA IgM is low, and that an isolated positive EIA IgM should prompt further follow-up and diagnostic testing.

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