INTERPRETATION OF POSTMORTEM VAGINAL ACID-PHOSPHATASE DETERMINATIONS

Identification of evidence indicative of sexual assault, including ele vated levels of acid phosphatase (AP) in the vagina, is an important p art of the investigation of female homicidal deaths. In this study, va ginal AP levels in 43 female homicide victims, determined using sodium thymolphthalein as the substrate, were retrospectively correlated wit h semiquantitative assessment of spermatozoa in vaginal smears. The re sults were then compared with those from a prospectively studied age-m atched group of controls. AP determinations ranged from 0 to 6,000 uni ts (U)/L in the homicide group and from 1 to 726 U/L in the control gr oup. In both groups, the majority of the AP values (homicide, 65%; and controls 85%) were < 100 U/L. Spermatozoa were identified on vaginal smears from 30% of the homicide victims and 17% of the controls. The s permatozoa-positive cases had AP levels that ranged from 2 to 6,000 U/ L. In both groups, an AP value of greater-than-or-equal-to 400 U/L was always associated with the presence of spermatozoa on the vaginal sme ar. Intermediate AP values (100-399 U/L) were associated with the pres ence of spermatozoa in 60% of the control group and 22% of the homicid e group; 18% of the homicide group and 3% of the control group were po sitive for spermatozoa despite AP values of < 100 U/L. In the absence of spermatozoa on a vaginal smear, an AP value of > 400 U/L strongly s uggests the presence of semen that is either oligo- or aspermic. A low or intermediate AP determination, however, does not exclude the prese nce of semen and hence a careful search for spermatozoa on the vaginal smear is indicated, regardless of the AP value obtained.