Specificity of Enzyme Immunoassay for Serologic Coccidioidomycosis Diagnosis Compared to Immunodiffusion

Abstract

BACKGROUND: Serologic testing for coccidioidomycosis challenges clinicians due to conflicting small studies regarding the sensitivity and specificity of newer enzyme immunoassay (EIA) tests and the lack of a true gold standard diagnostic test for comparison. METHODS: We analyzed all Lab Corp coccidioidomycosis serological test results from February 2008 through February 2009 and calculated the sensitivity, specificity, and positive/negative predictive values of EIA immunoglobulin (Ig)M and IgG. Immunodiffusion IgM and IgG (ID), complement fixation titers (CF), and tissue/culture diagnosis were used as tests for comparison. The comparison test (CT) was considered positive if any comparison test was positive the day of EIA collection or if tissue/culture diagnosis occurred during the time period. Cases required EIA IgM and IgG and ≥ 2 comparison tests performed the same day for inclusion. Medical records associated with positive EIA and negative comparison test results were reviewed for coccidioidomycosis symptoms, physician diagnosis, and subsequent positive comparison test results. Sensitivity, specificity, and predictive values were calculated, including those with subsequent positive comparison test results. RESULTS: A total of 1445 laboratory test sets were identified. EIA sensitivity and specificity were 83.8% and 92.6%, respectively. Positive and negative predictive values were 61.5% and 97.6%, respectively. Of 94 “false positive” EIA results, 92 (97.9%) were associated with documented coccidioidomycosis symptoms and 81% with coccidioidomycosis physician diagnosis. CONCLUSION: Based on the largest study of sensitivity and specificity calculated from laboratory surveillance data, EIA sensitivity and specificity for coccidioidomycosis diagnosis are lower than previously reported using only coccidioidomycosis laboratory tests as a comparison. However, association of “false positive” EIA results with coccidioidomycosis symptoms and physician diagnosis suggests that ID and CF laboratory tests alone are not a sufficient confirmation test for diagnosis.