An important proportion of genital samples submitted for Chlamydia trachomatis detection by PCR contain small amounts of cellular DNA as measured by beta-globin gene amplification.

We assessed the quality of genital samples submitted for Chlamydia trachomatis detection by PCR by a second PCR assay for the presence of human beta-globin DNA. Endocervical and urethral samples were first tested by the COBAS AMPLICOR C. trachomatis assay (Roche Diagnostic Systems) with an internal control and were then amplified for the presence of beta-globin DNA with primers PC04 and GH20. Samples that contained inhibitors were retested after dilution 1:10. A total of 407 genital samples (311 endocervical swabs from 311 women and 96 urethral swabs from 95 men and 1 woman) collected over a 1-month period were evaluated. The internal control could not be amplified, despite dilution, from 3 of 23 samples that were retested after dilution because of inhibition, leaving 404 samples that could be analyzed by PCR. Eleven samples tested positive for C. trachomatis. Thirty (7.4%) of the 404 samples were negative for beta-globin. Twelve of the 23 undiluted samples that contained inhibitors tested positive for beta-globin DNA. Amplification of beta-globin DNA in samples submitted for C. trachomatis detection by the COBAS AMPLICOR C. trachomatis assay demonstrated that an important proportion of the samples did not contain cellular DNA. Assessment of the quality of the samples for PCR analysis by beta-globin amplification is feasible but cannot replace use of the internal control.