A 1-year evaluation of Syva MicroTrak Chlamydia enzyme immunoassay with selective confirmation by direct fluorescent-antibody assay in a high-volume laboratory.
TThe Syva MicroTrak Chlamydia enzyme immunoassay (EIA; Syva Company, San Jose, Calif.) with cytospin and direct fluorescent-antibody assay (DFA) confirmation was evaluated on 43,630 urogenital specimens over a 1-year period in the Provincial Laboratory in Regina, Saskatchewan, Canada. This was a two-phase study intended to define a testing algorithm for Chlamydia trachomatis that would be both highly accurate and cost-effective in our high-volume (> 3,000 tests per month) laboratory. The prevalence of C. trachomatis infection in our population is moderate (8 to 9%). In phase 1, we tested 6,022 male and female urogenital specimens by EIA. All specimens with optical densities above the cutoff value and those within 30% below the cutoff value were retested by DFA. This was 648 specimens (10.8% of the total). A total of 100% (211 of 211) of the specimens with optical densities equal to or greater than 1.00 absorbance unit (AU) above the cutoff value, 98.2% (175 of 178) of the specimens with optical densities of between 0.500 and 0.999 AU above the cutoff value, and 83% (167 of 201) of the specimens with optical densities within 0.499 AU above the cutoff value were confirmed to be positive. A total of 12% (7 of 58) of the specimens with optical densities within 30% below the cutoff value were positive by DFA. In phase 2, we tested 37,608 specimens (32,495 from females; 5,113 from males) by EIA. Only those specimens with optical densities of between 0.499 AU above and 30% below the cutoff value required confirmation on the basis of data from phase 1 of the study. This was 4.5% of all specimens tested. This decrease in the proportion of specimens requiring confirmation provides a significant cost savings to the laboratory. The testing algorithm gives us a 1-day turnaround time to the final confirmed test results. The MicroTrak EIA performed very well in both phases of the study, with a sensitivity, specificity, positive predictive value, and negative predictive value of 96.1, 99.1, 90.3, and 99.7%, respectively, in phase 2. We suggest that for laboratories that use EIA for Chlamydia testing, a study such as this one will identify an appropriate optical density range for confirmatory testing for samples from that particular population.
Chan
E L
EL
Laboratory and Disease Control Services, Saskatchewan Health, Regina, Canada.
Brandt
K
K
Horsman
G B
GB
D000465:Algorithms; D002690:Chlamydia Infections / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D002692:Chlamydia trachomatis / Q000276:immunology / Q000302:isolation & purification*; D003363:Cost Control; D003720:Densitometry; D003955:Diagnostic Tests, Routine / Q000191:economics; D005069:Evaluation Studies as Topic; D005260:Female; D005455:Fluorescent Antibody Technique / Q000191:economics; D006801:Humans; D007124:Immunoenzyme Techniques / Q000191:economics; D008297:Male; D011237:Predictive Value of Tests; D015995:Prevalence; D011933:Reagent Kits, Diagnostic; D012525:Saskatchewan / Q000453:epidemiology; D012621:Seasons; D012680:Sensitivity and Specificity; D014526:Urethritis / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D002575:Uterine Cervicitis / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology
D011933:Reagent Kits, Diagnostic