Comparison of the effects of two presumptive test reagents on the ability to obtain STR profiles from minute bloodstains

Abstract

Background: Bloodstains often constitute the major physical evidence in criminal investi-gations. In many cases, the bloodstains found by the crime scene examiner are minute, possibly because of dissimulation efforts by the perpetrator to eliminate evidence that reveals his identity. In such cases, short tandem repeat (STR) detection procedures must be performed using the same minute bloodstain evidence on which presumptive tests had been performed earlier. In the present study, two of the most often used presumptive test reagents, phenolphthalein and leucomalachite green, were tested to determine their effects on the ability to obtain STR profiles from minute bloodstains. Methods: Dried minute bloodstains obtained from 10 donors were treated with phenolphthalein and leucomalachite green. After various times, genomic DNA was extracted from the treated samples using a QIAamp DNA Micro Kit. DNA was quantified with real-time PCR using a Quantifiler Kit. STR loci were amplified using an AmpFLSTR Identifiler Plus Kit, and the amplified products were separated via capillary electrophoresis in a 3130 Genetic Analyzer. Results: Full DNA profiles were obtained from all minute bloodstain samples treated with phenolph-thalein when extracted after intervals ranging from 1 h to 1 week. In contrast, the DNA in minute bloodstain samples treated with leucomalachite green was severely degraded, especially after relatively long intervals, leading to poor partial DNA profiles. Conclusion: Phenolphthalein is recommended as a safe presumptive test reagent for the detection of blood evidence recovered from crime scenes that might subsequently undergo DNA profiling analysis.

Keywords

• Minute bloodstain
• Presumptive test reagent
• Phenolphthalein
• Leucomalachite green
• STR profiling