URINARY INHIBITORS OF POLYMERASE CHAIN-REACTION AND LIGASE CHAIN-REACTION AND TESTING OF MULTIPLE SPECIMENS MAY CONTRIBUTE TO LOWER ASSAY SENSITIVITIES FOR DIAGNOSING CHLAMYDIA-TRACHOMATIS INFECTED WOMEN

In a comparison of commercial ligase chain reaction (LCR; Abbott) and polymerase chain reaction (PCR; Roche) assays, measuring plasmid genes of Chlamydia trachomatis, some specimens were found to be negative by either or both assays but positive in traditional culture or antigen detection tests. Of 767 women, 35 were found to be infected by cervica l or urine testing. Twenty three specimens from 16 women may have cont ained inhibitors in six cervical swabs (CS) and 15 first void urines ( FVU). By performing dilution and 'spiking' experiments on five FVU, in hibitors of PCR, LCR or both, which disappeared by dilution, were demo nstrated. Confirmatory assays were used which amplified segments of th e major outer membrane gene by PCR or LCR. When comparisons of assays were made on a single specimen type, the sensitivities of the amplific ation assays, compared to an expanded reference standard, were as foll ows: on CS, PCR was 93.8% (30/32) and LCR was 96.9% (31/32); on FVU, P CR was 76.6% (23/30) and LCR was 93.3% (28/30). When a combined calcul ation was made to determine the ability of the assays to detect patien ts infected in the cervix or urethra by testing FVU, the sensitivities dropped to 71.4% (25/35) for PCR and 80.0% (28/35) for LCR: CS sensit ivity was 88.6% (31/35) for both amplified tests. There were two CS an d five FVU false-positives by PCR which reduced to one CS and three FV U in the combined analysis. There were no false-positives by LCR. Inhi bitors and low levels of chlamydial plasmid nucleic acids may have con tributed to lower than expected sensitivities, suggesting a possible n eed for internal positive controls, especially for PCR when testing ur ine. More studies with multiple sampling and more than one amplificati on assay are needed to confirm these findings and to identify and remo ve inhibitors of amplification assays. (C) 1997 Academic Press Limited .