Evaluating the sensitivity of presumptive and confirmatory tests for body fluids

Abstract

Most exhibits received in the forensic genetics laboratory of Ras Al Khaimah (United Arab Emirates) are swabs or clothing with stains suspected of being either blood, semen or saliva; swabs from touch DNA are also reasonably common. Routine practice has been to use presumptive tests to characterize the materials before DNA extraction. In this study we evaluated the presumptive methods currently used for blood (Hemastix® and Kastle-Meyer), semen (Phosphatesmo KM) and saliva (Phadebas®) in comparison to the confirmatory tests OBTI Hexagon and RSID™ Blood, RSID™ Semen and RSID Saliva™. Results from this study showed that, as expected, presumptive tests were generally more sensitive in detecting body-fluids than confirmatory tests. The presumptive tests were at least two-fold more sensitive than the RSID™ Blood, Semen and Saliva confirmatory tests. However, the OBTI Hexagon test showed comparable sensitivity to Kastle-Meyer and Hemastix® for the detection of blood; this test utilizes an anti-hemoglobin antibody, which enables the high level of sensitivity. DNA was extracted from different dilutions and quantified using real-time PCR with the Quantifiler™ Human kit. Except for the RSID™-Blood and Saliva, the limit of detection for the tests was at dilutions where recovery of sufficient DNA for STR analysis was not likely.