Prostate-specific antigen in vaginal fluid after exposure to known amounts of semen and after condom use: comparison of self-collected and nurse-collected samples.

BACKGROUND: Prostate-specific antigen (PSA) in vaginal fluid indicates exposure to semen, and was used to assess condom effectiveness, although validity and reliability have not been fully evaluated. Our objective was to compare PSA in self-collected samples with samples collected by a nurse.
METHODS: We conducted two studies, each with 100 women aged 18-48 years. In the first, a nurse exposed each participant to her partner's semen (10, 100 and 1000 microl), and nurse and participant collected samples. In the second, each participant sampled before and after using two male condoms (MC) and two female condoms (FC); a nurse collected another sample afterwards.
RESULTS: PSA concentration increased with semen exposure, but was lower in nurse-collected samples. Both procedures were sensitive, almost 100% after exposure to 100-1000 microl of semen. PSA detection rates with MC and FC were 13% and 28% in self-collected samples, 8% and 9% in nurse-collected samples. Concordance between sample types was 93% with the MC (95% CI: 89%; 96%), 78% with the FC (95% CI: 72%; 84%). PSA decay between sampling times may explain higher values in self-collected samples.
CONCLUSIONS: PSA is a highly sensitive surrogate endpoint for condom effectiveness studies. Self-collected and nurse-collected samples are equivalent, but sample collection timing is critical.