Postcoital Detection of a Male-Specific Semen Protein

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Abstract
Identification of semen in vaginal fluid may provide documentation of sexual contact in alleged victims of rape. We describe an enzyme-linked immunosorbent assay for a semen glycoprotein of prostatic origin, designated p30. This test detects as little as 3 ng of the p30 antigen per milliliter in various body fluids. Semen from normal and vasectomized men contains high levels of p30 (mean, 1.55 mg per milliliter of seminal plasma), and urine from men contains low levels (mean, 260 ng per milliliter). However, the antigen cannot be detected in body fluids from women, including vaginal fluid and urine, suggesting that p30 may be a male-specific antigen. The p30 antigen was detectable in vaginal fluid for a mean period of 27 hours after coitus, as compared with 14 hours for prostatic acid phosphatase. Of 27 vaginal fluid samples from women who were allegedly raped in which the acid phosphatase test was negative, 7 (26 per cent) were unequivocally positive for p30 by our assay. We conclude that the assay for p30 offers a more sensitive and specific method of semen detection in rape investigation than the enzyme assay for prostatic acid phosphatase. (N Engl J Med 1985; 312:338–43.)