LOWERING THE CUT-OFF VALUE OF AN AUTOMATED CHLAMYDIA ENZYME-IMMUNOASSAY AND CONFIRMATION BY PCR AND DIRECT IMMUNOFLUORESCENT ANTIBODY-TEST

Aims-To increase the sensitivity of an automated chlamydia enzyme immu noassay by significantly lowering its cut off value, and to maintain s pecificity by confirmation with polymerase chain reaction (PCR) and di rect immunofluorescent antibody test (DFA). Methods-Over five months, the cut off value of the enzyme immunoassay used to screen urogenital samples for chlamydia antigen was reduced from 80 to 10. Samples with a test value of 10 or above were further tested with a commercial PCR assay. All samples during the first three months and discrepant sample s during the last two months of the study were also tested with the DF A. Results-3250 urogenital swabs (1246 urethral, 1335 endocervical, 66 9 pooled urethral/endocervical) from 1246 males and 2004 females were processed. Using the manufacturer's recommended cut off of 80, the enz yme immunoassay identified chlamydia antigen in 134 samples (4.1%). Us ing the lower cut off value of 10 and either PCR or DFA as the confirm atory test, Chlamydia trachomatis was identified in 178 samples (5.5%) . Thus, 45 additional postive samples were identified and the confirme d detection rate was increased by 33.8% (45/133). Excluding equivocal PCR results, the concordance between DFA and PCR was 91.8%. This strat egy increased the detection rate by 2.1% in men and 0.9% in women (sig nificant only in men). In female patients, pooled urethral/endocervica l swabs as a specimen gave a significantly higher yield than endocervi cal swabs regardless of whether the lower cut off strategy was used. C onclusions-This strategy of significantly lowering the cut off test va lue with confirmation on the same specimen by either PCR or DFA is fea sible and cost effective. The use of pooled urethral/ endocervical spe cimens in females should be considered routinely as detection rate was significantly improved.