URINE SPECIMENS FROM PREGNANT AND NONPREGNANT WOMEN INHIBITORY TO AMPLIFICATION OF CHLAMYDIA-TRACHOMATIS NUCLEIC-ACID BY PCR, LIGASE CHAIN-REACTION, AND TRANSCRIPTION-MEDIATED AMPLIFICATION - IDENTIFICATION OFURINARY SUBSTANCES ASSOCIATED WITH INHIBITION AND REMOVAL OF INHIBITORY ACTIVITY

The presence of endogenous amplification inhibitors in urine may produ ce false-negative results for the detection of Chlamydia trachomatis n ucleic acids by tests such as PCR, ligase chain reaction (LCR), and tr anscription-mediated amplification (TMA), Consecutive urine specimens from 101 pregnant women and 287 nonpregnant women submitted for urinal ysis were processed for C, trachomatis detection. Aliquots were spiked with the equivalent of one C, trachomatis elementary body and were te sted by three commercial assays: AMPLICOR CT/NG, Chlamydia LCX, and Ch lamydia TMA, The prevalence of inhibitors resulting in complete inhibi tion of amplification was 4.9% for PCR, 2.6% for LCR, and 7.5% for TMA , In addition, all three assays were partially inhibited by additional urine specimens. Only PCR was more often inhibited by urine from preg nant women than by urine from nonpregnant women (9.9 versus 3.1%; P = 0.011), A complete urinalysis including dipstick and a microscopic exa mination was performed, Logistic regression analysis revealed that the following substances were associated with amplification inhibition: b eta-human chorionic gonadotropin (odds ratio [OR], 3.3) and crystals ( OR, 3.3) for PCR, nitrites for LCR (OR, 14.4), and hemoglobin (OR, 3.3 ), nitrites (OR, 3.3), and crystals (OR, 3.3) for TMA. Aliquots of eac h inhibitory urine specimen were stored at 4 and -70 degrees C overnig ht or were extracted with phenol-chloroform and then retested at dilut ions of 1:1, 1:4, and 1:10, Most inhibition was removed by storage ove rnight at 4 or -70 degrees C and a dilution of 1:10 (84% for PCR, 100% for LCR, and 92% for TMA), Five urine specimens (three for PCR and tw o for TMA) required phenol-chloroform extraction to remove inhibitors. The results indicate that the prevalence of nucleic acid amplificatio n inhibitors in female urine is different for each technology, that th is prevalence may be predicted by the presence of urinary factors, and that storage and dilution remove most of the inhibitors.