FALSE-NEGATIVE RESULTS OF A LIGASE CHAIN-REACTION ASSAY TO DETECT CHLAMYDIA-TRACHOMATIS DUE TO INHIBITORS IN URINE

The aim of this study was to assess the presence of inhibitors in urin e specimens causing false-negative results in a commercial Chlamydia t rachomatis gap-filling ligase chain reaction (Gap-LCR) assay. On testi ng of urine samples by the Gap-LCR assay and urethral swab specimens b y cell culture, 73 (19%) Chlamydia trachomatis positive subjects were detected among 382 men attending a clinic for sexually transmitted dis eases, In 56 subjects, the agent was detected in both the urine and th e urethral samples, while 309 subjects were negative in both tests, In seven subjects urine samples were Gap-LCR positive (confirmed by a di fferent Gap-LCR assay), but the corresponding urethral swab samples we re cell culture-negative. In another ten subjects the urethral swab sa mples were cell culture positive, but their urine samples were Gap-LCR negative, Subsequent re-analysis of the urine samples including the a ddition of external Chlamydia trachomatis DNA indicated full or partia l inhibition in nine of the cell culture-positive Gap-LCR negative sub jects. When urine preparations were freeze-thawed and diluted prior to testing, Chlamydia trachomatis was detected in six of the ten initial ly Gap-LCR-negative samples. Gap-LCR inhibitors were present in at lea st nine (12%) of the 73 urine preparations from the Chlamydia trachoma tis positive individuals, Identification of samples containing Gap-LCR inhibitors and subsequent processing to reduce the inhibition increas ed the sensitivity of the test from 86% to 95%.