EVALUATION OF VERIFICATION ASSAYS IN EIA SPECIMENS PRESUMPTIVELY POSITIVE FOR CHLAMYDIA-TRACHOMATIS

Verification of specimens positive for Chlamydia trachomatis by enzyme immunoassay (EIA) has been recommended when testing low prevalence po pulations. This study compared direct fluorescent antibody (DFA) and b locking antibody (BLA) verification assays in specimens presumptively positive for C. trachomatis by the Syva Microtrak II EIA. Of 1785 spec imens originally tested by EIA, 96 were presumptively positive for C. trachomatis. Verification assays were concordant in 86 specimens (69 p ositive, 17 negative); nine of the remaining samples gave positive res ults in a second EIA and one was unresolved. Both verification assays gave some false-negative results. When initial EIA absorbance values w ere correlated with verified results, all EIA false positive results h ad absorbances in the low range (less than a three-fold increase over assay cutoff values). Verification of EIA results by both DFA and BLA was effective in detecting false positive results, but confining verif ication to low-value positive specimens could be considered for cost-e ffective C. trachomatis testing.