The identification of human semen by a chemiluminescent assay of choline

A method for proving the presence of semen has been established by utilizing chemiluminescence for an assay of choline, a nonprotein constituent of semen, and medicolegal testings were carried out to evaluate its effectiveness. The sensitivity of this method to choline was 3 nmol/ml, and as a result of assays of the choline content in semen and in several other human body fluids and secreta, the choline level in semen was found to be 10.88-26.78 mumol/ml (mean = 16.69 +/- 4.01 mumol/ml), which was markedly higher. The choline content in semen specimens from subjects with oligospermia or azoospermia was similarly as high. Although choline was also detected in samples of certain dairy products, vegetable juice, and fruit juice, whose stains are almost indistinguishable from semen to the naked eye, the choline content in these specimens was much lower than in semen. Further, even when human semen specimens were heated to 100 degrees C for 30 min and seminal stains were heated to 200 degrees C for 30 min, the choline content still retained 71.6% and 66.9% of the pre-heating value, respectively. As for specimens of semen and seminal stains that were stored at room temperature for 12 months, about 1/3 and 1/2 of the original choline level were detected, respectively. Also, the presence of intravaginal drugs was shown to have no large influence on the detection of choline. Choline even could be detected in aged seminal stains stored for 11 years, so that the presence of semen was demonstrated. Finally, the presence of semen in the vaginal contents, collected on medicolegal autopsy, could also be demonstrated by the detection of choline. Thus utilizing chemiluminescence for detecting choline is considered useful for establishing medicolegal proof of the presence of semen.