Lactate dehydrogenase isozymes in vaginal swab extracts: a problem for the identification of menstrual blood.

Extracts of vaginal swabs free of both blood and semen, collected from three donors throughout several menstrual cycles, have been examined by cellulose acetate membrane electrophoresis for the presence of lactate dehydrogenase (LDH) isozymes. LDH activity, predominantly in the form of LDH-5 was detected in some extracts. Mixtures of these particular extracts with peripheral blood gave LDH patterns similar to those observed for menstrual blood. The results indicate that LDH isozyme patterns cannot be used to differentiate between stains of menstrual blood and bloodstains that have become mixed or contaminated with vaginal secretions.