Evaluation of a commercial enzyme immunoassay versus culture for the detection of Chlamydia trachomatis.

A commercial EIA (Chlamydiazyme) for detection of Chlamydia trachomatis was evaluated in comparison to culture using genital specimens from 472 men and 279 women. The sensitivity of the EIA compared with culture was 66.0% in men and 71.4% in women, while the specificity was 99.7% and 95.9% respectively. The EIA failed more often to detect chlamydial antigen when the number of inclusion bodies found in the corresponding cultures was less than or equal to 100/well. A direct test (MicroTrak) was performed on the EIA samples which showed discordant results compared to corresponding cultures. One of 17 EIA positive samples, and 12 of 36 EIA negative samples were positive in the direct test (p less than 0.05). A cut-off absorbance value of 0.1 is recommended by the manufacturer in the EIA. However, 84.2% of the EIA negative samples in the negative absorbance interval 0.05-0.099 corresponded with a positive culture. In view of variations in the sensitivity of the culture technique between laboratories and the low sensitivity of the EIA found in this study, it is recommended that each laboratory using the EIA compare it to culture. It is also recommended that an equivocal zone around the cut-off value be used in the EIA, the zone to be established by each laboratory using the test.