EFFECTS OF TOLUIDINE BLUE AND DESTAINING REAGENTS USED IN SEXUAL ASSAULT EXAMINATIONS ON THE ABILITY TO OBTAIN DNA PROFILES FROM POSTCOITALVAGINAL SWABS

Toluidine blue is an important tool to detect and document genital and perianal injuries following sexual assault. Application of toluidine blue dye and its subsequent removal from unstained areas by means of a destaining reagent, such as diluted acetic acid or a lubricant has be en shown to increase the detection rate of posterior fourchette lacera tions from 16% to 40% in adult rape victims. Currently, limited inform ation on toluidine blue positive findings in sexually active control g roups imposes some limitation on the interpretation of these injuries. Because injuries could otherwise be attributed to improper handling o f an examination speculum or the improper insertion of the examining f inger, the toluidine blue test should be performed prior to any digita l or speculum examination and thus prior to the collection of forensic evidence. For forensic DNA identity testing, it becomes pertinent to determine whether toluidine blue and the destaining reagents used in a sexual assault examination have an adverse effect on the recovery of high molecular weight DNA from postcoital vaginal swabs and thereby ha ve an impact on restriction fragment length polymorphism (RFLP) analys is or PCR-based tests. It is known that some of the lubricants used ca n have a destructive effect on sperm motility. In order to investigate the potential effects, postcoital vaginal swabs were taken 6 h after sexual intercourse and exposed directly to 1% toluidine blue in aqueou s solution, 1-10% acetic acid, and various surgical and vaginal lubric ants. Subsequently, the DNA was isolated and DNA identity typing (RFLP and PCR-based) was performed. The results demonstrate, that these rea gents have no negative effect on the ability to obtain DNA profiles, e ither RFLP or PCR-based, from shallow and deep vaginal swabs. The quan tity and quality of extractable high molecular weight DNA obtained was comparable with that from uncontaminated postcoital vaginal swabs. RF LP patterns and PCR-based typing results on the D1S80, HUMTH01, TPOX, and CSF1PO loci were consistent with the uncontaminated control swabs and the corresponding whole blood samples of the donors. Therefore, ev identiary material inadvertently contaminated with these reagents can be successfully typed.