Prostate-specific antigen is unlikely to be a suitable biomarker of semen exposure from recent unprotected receptive anal intercourse in men who have sex with men.

A biomarker of unprotected receptive anal intercourse (RAI) could improve validity of sexual behavior measurement. We quantified prostate-specific antigen (PSA) from rectal swabs from men who have sex with men (MSM). One swab was PSA-positive. Using current methods, PSA is an inadequate biomarker of recent unprotected RAI in MSM.