Integrating presumptive and confirmatory semen tests into DNA profiling of sexual assault evidence: a Philippine example

Background In sexual assault casework, the detection of semen on a sample supports an allegation of sexual contact and indicates the presence of DNA from a male source. Ideally, techniques employed should demonstrate high sensitivity and specificity and should be compatible with standard DNA typing procedures. To contribute recommendations for routine DNA tests of sexual assault cases in the Philippines, we evaluated the RSID TM -Semen, an immunochromatographic test for human semenogelin (Sg), in parallel with the alternate light source (ALS) method using Mini BLUMAXX™ III and the acid phosphatase (AP) test using Seminal Fluid DISCHAPS TM . Results The ALS detected semen diluted until 5% ( v / v ) fluid, whereas the AP assay was sensitive down to 0.5% ( v / v ). Non-blood-containing stains were visible under blue light except on dark-colored cloth. All semen-containing fluids including post-ejaculatory urine tested positive for AP and Sg. RSID TM -Semen was sensitive down to 0.5 nL of semen; did not cross-react with blood, saliva, and female urine; and successfully detected Sg on the majority of post-coital samples tested. Complete short tandem repeat (STR) profiles of the semen donors were generated for most samples incubated in the RSID TM -Universal Buffer (UB). However, we report an extraction efficiency of 15% for UB which can lead to partial profiles in already compromised samples. Conclusion We recommend the use of ALS in visualizing stains present on surfaces and the AP test on blood-stained materials. These presumptive tests should be followed by RSID TM -Semen test to confirm the presence of semen prior to DNA profiling.