Evaluation of the Gen-Probe PACE 2 and the Microtrak Enzyme Immunoassay for Diagnosis of Chlamydia trachomatis in Urogenital Samples

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Abstract
The aim of the study was to investigate the value of the Gen-Probe PACE 2 assay for routine diagnosis of Chlamydia trachomatis in genital specimens of symptomatic and asymptomatic men and women patients. Samples were collected from 90 men and 299 women patients and tested by using the Gen-Probe assay and the EIA MicroTrak. Discrepant results were further analyzed by immunofluorescence, a second run of the Gen-Probe assay, and a probe competition assay (PCA) to establish the number of true positive and negative outcomes based on the two tests used. The overall prevalence of C. trachomatis was 8.5% in all patients tested (women: 3.7%, men: 13.3%) with an overall agreement of 95.4% between the two diagnostic methods. Of the 18 discordant results, 12 (67%) were considered to be false positive in the Gen-Probe assay and 3 (16%) false positive in the EIA. Two (11%) positive results were missed in the Gen-Probe assay and 1 (6%) in the EIA, all observed in female specimens. The sensitivities and specificities of the EIA were 91.7% and 100% for men and 100% and 99% for women, and for the Gen-Probe assay were 83.3% and 100% for men and 100% and 95.8% for women, respectively, when compared with true positive and true negative results. Although the predictive value for all positive results (PVP) was 88% for the EIA and 78.2% for the Gen-Probe assay, it was only 47.8% for positive female samples when using the Gen-Probe assay. The Gen-Probe assay revealed a sensitivity comparable with the EIA. The accuracy of test results provided by a single Gen-Probe assay was considerably lower than by Micro-Trak reducing the utility of PACE 2 as a diagnostic technique for Chlamydia diagnosis. Due to the high rate of false-positive samples in the Gen-Probe assay, positive results with a low value of relative light units have to be further analyzed by confirmation procedures.

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