Background: Studies of condom efficacy rely on self-reported behavior. Objective markers of exposure to semen may provide a more valid assessment of condom failure and failure to use condoms.
Goals of this study: To compare three semen biomarkers: acid phosphatase (AP) activity, prostate specific antigen (PSA), and the human seminal plasma antigen (MHS-5).
Study design: Twenty women were intravaginally inoculated with six measured, increasingly larger amounts of their partners' semen. Vaginal fluid was collected by the participant using swabs and tested.
Results: Background levels of PSA were low (0.00-1.25 ng/ml), background levels of AP were variable (0-350 U/l), and all preinoculation samples were negative for MHS-5. All postinoculation samples were positive for PSA, 64 of 117 (55%) for AP, and 14 of 120 (12%) for MHS-5.
Conclusion: The PSA immunoassay was the best semen biomarker under these sampling and testing conditions.
PIP: Objective markers of exposure to semen provide a more valid assessment of condom failure and failure to use condoms than self-reports. The present study evaluated three of the assays commonly used in forensic medicine for detecting semen exposure: acid phosphatase (AP) activity, prostate specific antigen (PSA), and the human seminal plasma antigen (MHS-5). 20 US women were intravaginally inoculated with 6 measured, increasingly larger amounts of their partners' semen. Vaginal fluid was collected with swabs by study participants and tested for the three markers. Before semen inoculation, PSA levels were consistently low (median, 0.11 ng/ml; range, 0-1.25 ng/ml) while those of AP were highly variable (median, 13.4 U/l; range, 0-350 U/l); all preinoculation samples were negative for MHS-5. The median PSA concentration increased consistently with increasing volumes of semen, while median AP and MHS-5 levels showed an inconsistent pattern. All 120 swabs obtained after intravaginal inoculation with semen were positive for PSA, 64 (55%) were positive for AP, and 14 (12%) were positive for MHS-5. These findings indicate that self-sampling of vaginal secretions followed by the PSA immunoassay represents a simple, accurate marker of semen exposure. Because the PSA assay is available in most hospital laboratories for prostate cancer screening, the methodology used in the present study is suitable for widespread application.