Background Prostate Specific Antigen (PSA) and Y chromosome are used as biomarkers of semen exposure. There is currently no information on whether vaginal products evaluated in microbicide trials, in particular, tenofovir gel (TFV), UC781 or the universal HEC placebo (hydroxyethylcellulose) affect the detection of these markers.

Methods Dilutions of TFV, UC781, and the universal HEC placebo, combined with semen, were tested for PSA using both the Abacus ABAcard semi-quantitative and the Abbott Architect quantitative assay. Y chromosome DNA was determined by real-time polymerase chain reaction (real-time PCR).

Results Tenofovir gel and the universal HEC placebo adversely affected PSA detection using the ABAcard, but not the Abbott Architect PSA assay. UC781 affected PSA results by ABAcard and, at all dilutions, caused invalid results for Abbott Architect assay. None of the products substantially affected the Y chromosome PCR assay’s indication of presence of Y chromosome DNA, but the quantitative results varied by product.

Conclusions These in vitro results indicate that the Abbott Architect assay, rather than the ABAcard, should be used for PSA detection when tenofovir gel or the universal HEC placebo might be present. The Y chromosome PCR assay when used qualitatively to indicate presence of Y chromosome is not affected by any of these products, but the quantitative results should be used cautiously as the values are affected by microbicide products. In vivo confirmation of these findings is recommended to further optimise detection of semen biomarkers when microbicide products may be used.