Vaginal fluid zinc concentration as a marker for intercourse

Zinc is present in high concentration in semen, but in low concentration in vaginal fluid. We evaluated vaginal zinc levels as a marker for intercourse by measuring precoital (greater than 11 h after intercourse) or postcoital (less than 5 h after intercourse) zinc and acid phosphatase levels in 26 specimens of vaginal fluid from 18 women. The approximate 95% reference range for zinc in precoital vaginal fluid was 1.2 to 15 micrograms/mL (mean 4.5), and in postcoital vaginal fluid 4.0 to 135 micrograms/mL (mean 24). There is an overlap between the precoital and postcoital reference ranges. Provided that the vaginal fluid zinc level is less than approximately 4.0 micrograms/mL or greater than approximately 15 micrograms/mL, vaginal fluid zinc concentration may be useful as an indicator of intercourse.