Forensic differentiation between peripheral and menstrual blood in cases of alleged sexual assault-validating an immunochromatographic multiplex assay for simultaneous detection of human hemoglobin and D-dimer

Abstract

Sexual assault is a serious offense and identification of body fluids originating from sexual activity has been a crucial aspect of forensic investigations for a long time. While reliable tests for the detection of semen and saliva have been successfully implemented into forensic laboratories, the detection of other body fluids, such as vaginal or menstrual fluid, is more challenging. Especially, the discrimination between peripheral and menstrual blood can be highly relevant for police investigations because it provides potential evidence regarding the issue of consent. We report the forensic validation of an immunochromatographic test that allows for such discrimination in forensic stains, the SERATEC PMB test, and its performance on real casework samples. The PMB test is a duplex test combining human hemoglobin and D-dimer detection and was developed for the identification of blood and menstrual fluid, both at the crime scene and in the laboratory. The results of this study showed that the duplex D-dimer/hemoglobin assay reliably detects the presence of human hemoglobin and identifies samples containing menstrual fluid by detecting the presence of D-dimers. The method distinguished between menstrual and peripheral blood in a swab from a historical artifact and in real casework samples of alleged sexual assaults. Results show that the development of the new duplex test is a substantial progress towards analyzing and interpreting evidence from sexual assault cases.

Keywords: Body fluid identification; D-dimer; Immunochromatographic assay; Menstrual blood; Sexual assault.

Fig. 1

Examples for a positive peripheral blood test (a) and positive menstrual fluid test (b). The peripheral blood test shows a positive hemoglobin (P) signal and no false-positive D-dimer (M) signal. Menstrual blood reacts positive for hemoglobin (P) and D-dimer (M). The negative control (c) shows no signal for hemoglobin or D-Dimer. A signal for correct test performance (C) is present in all three examples

Fig. 2

Heat maps of a signals for D-dimer presence with the 300 and 400 ng/ml cut-off (donor 1 to 16 = dried blood, donor 17 = liquid blood), b the sensitivity study, c the mixtures and cross-reactivity testing, d blood collected from aged donors, and e postmortem blood samples. MB menstrual blood, PB peripheral blood, VF vaginal fluid