Evaluation of latex agglutination tests for fibrin-fibrinogen degradation products in the forensic identification of menstrual blood

The identification of menstrual blood is important when discriminating menstruation from vaginal trauma in sexual assault cases. The aim of this study was to evaluate two fibrin-fibrinogen degradation product (FDP)- latex agglutination test kits, FDPL® Test (FDP-L) and FDP Plasma “RD” (FDP-P), for their ability to forensically identify menstrual blood. Sensitivity and specificity of the two kits were compared for menstrual blood and various body fluids, and the sensitivity of the FDP-latex agglutination test kit was also compared with that of an immunochromatographic test for human haemoglobin. The robustness of the FDP-latex agglutination test was compared with that of gene expression analysis of menstrual blood-specific markers. The FDP-L kit was more sensitive than the FDP-P kit, but it cross-reacted with peripheral bloodstains from healthy volunteers. The FDP-P kit was specific for menstrual blood, with the exception of postmortem blood samples, and was not affected by other body fluids. In an FDP-negative menstrual blood sample, the sensitivity of human haemoglobin detection was lower than for FDP-positive samples and peripheral blood stains, suggesting that determination of human haemoglobin could be useful in interpreting negative results in the FDP-latex agglutination test. In menstrual blood samples incubated in wet conditions, FDP was found to be a robust marker in the identification of menstrual blood compared with mRNA markers. FDP-P testing was shown to be a suitable and highly efficient rapid screening test for the laboratory identification of menstrual blood.