Evaluation of DNA Extraction Efficiencies of Promega’s DNA IQ™ Methods and Casework Extraction Kit for Low Template Samples

Biological evidence from crime scene samples frequently contain low levels of DNA, such as the most predominant form of evidence, which is DNA deposited by handling objects or “touch evidence”. To maximize the DNA yield recovered from theses challenging samples, forensic laboratories must optimize the extraction methods utilized to isolate and purify DNA for downstream short tandem repeat (STR) amplifications. Currently, the Virginia Department of Forensic Science (VADFS) uses a DNA IQ™ System (DNA IQ) extraction method for isolation of DNA from most forensic samples. This extraction procedure, which combines DNA IQ™ lysis buffer and Dithiothreitol (DTT), has been validated for nearly every forensic casework sample other than sexual assault samples requiring differential extraction, hair roots, and bone. In 2004, VADFS created an in-house proteinase K buffer (IQP) to be utilized in conjunction with the DNA IQ™ System for hair, concentrated bloodstains, and other difficult samples believed to contain low quantities of DNA. The IQP extraction method was implemented at VADFS for lower template samples but also to digest hemoglobin found in concentrated bloodstains, as undigested proteins from these sample types had been observed to competitively bind to the DNA IQ™ resin, thus occluding it from binding DNA. In this study, the current methods utilized by VADFS for the extraction and purification of DNA with the DNA IQ™ System were evaluated against Promega Corporation’s Casework Extraction Kit (CEK). Similar to IQP, the CEK contains a proteinase K treatment step prior to DNA purification using the DNA IQ™ System. DNA yields and STR profiles obtained from a variety of low-template samples including diluted blood and saliva, environmental samples, hair, cigarette butts, and touch DNA samples were compared across these three extraction procedures. This research found that all three extraction methods produced comparable results for the extraction of anagen/catagen hair roots and cigarette butts. The in-house proteinase K extraction method provided significantly lower DNA yields and percent profiles for diluted blood and saliva samples, environmental samples, and touch samples, when compared to the CEK and the DNA IQ extraction methods. The Casework Extraction Kit demonstrated higher DNA yields and percent profiles for diluted blood and saliva samples when compared to DNA IQ and IQP methods. The CEK also yielded higher average DNA concentrations for the degraded bloodstain samples, however, the DNA IQ method produced consistent STR profiles with those extracted using the CEK. The DNA IQ and CEK extraction methods demonstrated overall superior performance over the IQP method for extraction of DNA from touch samples. The results of this study provide confirmation that the utilization of the DNA IQ extraction method for isolation of DNA from challenging casework samples is comparable to, and sometimes outperforms, the Casework Extraction Kit and should therefore be maintained as the primary DNA extraction method when purifying samples using the DNA IQ™ System