Chlamydial antigen detection in urine samples by immunofluorescence tests

To investigate the diagnostic value of a direct immunofluorescence test (DIF-test), urethral samples and first catch urine (FCU) from 153 male patients attending an outpatient clinic for sexually transmitted diseases (STD) were studied. Of the male patients, 40 (26.1%) had a positive urethral culture, 39 (25.5%) had a positive urethral DIF-test, and 32 (20.9%) were positive in urine according to the DIF-test. The sensitivity and the specificity of the DIF-test in male urine specimens were 75% and 98.2%, respectively, as compared with the chlamydial culture, and 69.2% and 95.6%, respectively, as compared to the DIF-test of the urethral samples. Out of the positive urethral samples, 31% had less than 5 elementary bodies (EBs) and 41% greater than 10 EBs, detected by the DIF-test. The corresponding data for FCU were 47% and 22%, indicating a smaller number of chlamydiae in urine than in urethral samples. False negative results in the urine DIF-test were mostly observed in males with a low number of EBs in the urethra. The DIF-test was less sensitive for FCU than for urethral specimens. Therefore, urine DIF-tests cannot replace conventional methods for chlamydial diagnosis in symptomatic STD patients, but may be recommended when genital sampling is not possible and may serve as an important approach in the control of genital chlamydial infections.