Development of a multiplex reverse transcription qPCR assay for identification of saliva, blood, and semen

The identification of body fluids can provide important information for case processing in forensic investigations. Accurate identification through messenger RNA (mRNA) is effective, especially in cases of sexual assault, where body fluids from one or more contributors are mixed. In this study, a saliva, blood, and semen simultaneous identification reverse transcription-quantitative polymerase chain reaction (SBS RT-qPCR) assay using mRNA from a DNA/RNA co-extraction method was developed. The body fluid-specific mRNA markers histatin 3 (HTN3), haemoglobin subunit beta (HBB), and protamine 1 (PRM1) were selected for identification of saliva, blood, and sperm cells, respectively. The assay accurately identified saliva, blood, and semen without cross-reaction with 10 body fluids. The limits of detection (LoD) were 1/10²-, 1/10⁵-, and 1/10³-fold dilutions of total RNA in saliva, blood, and semen, respectively. Furthermore, the assay accurately identified trace amounts of body fluids in mixed samples at a 58:1:1 ratio. Finally, it was possible to analyse the origin of body fluids by obtaining an STR profile using the DNA/RNA co-extraction method. The SBS RT-qPCR assay was able to simultaneously identify each body fluid with efficiency in sample consumption. Therefore, it is advisable to use the DNA/RNA co-extraction method to identify mixed body fluids in sexual assault cases.