Evaluation of the Gen-Probe PACE 2 and the Microtrak enzyme immunoassay for diagnosis of Chlamydia trachomatis in urogenital samples

Sex Transm Dis. Jan-Feb 1994;21(1):26-30. doi: 10.1097/00007435-199401000-00006.


Background and objectives: 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.

Study design: 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.

Results: 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.

Conclusion: 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.

MeSH terms

  • Chlamydia Infections / diagnosis*
  • Chlamydia trachomatis*
  • Evaluation Studies as Topic
  • False Positive Reactions
  • Female
  • Humans
  • Immunoenzyme Techniques
  • Male
  • Sensitivity and Specificity