Direct PCR of Forensic Evidence: Making the Case to Modify the Quantification Requirement

Direct polymerase chain reaction (PCR) is a method in which a swab or substrate punch is added to an amplification reaction without prior extraction or quantification and has been shown to improve DNA profiles from some types of low-yield DNA evidence samples. Direct PCR maximizes the amount of DNA template in a reaction by eliminating the DNA loss that occurs during DNA extraction, quantification, and concentration. It can also reduce laboratory errors, contamination events, sample processing time, and costs.

Use of direct PCR on forensic reference samples began in the mid–2000s with the release of commercial direct STR amplification kits, which have been demonstrated to be reliable, efficient, and cost effective for high-throughput processing. Application of direct PCR to evidentiary-type samples began in 2010 when Linacre et al. evaluated direct PCR on worn clothing items. Over the last decade, research examining direct PCR for forensic evidence samples has expanded to include many biological materials, substrates, and collection methods. Successes observed in this research have led to interest in implementing direct PCR for casework. In 2014, Forensic Science Service Tasmania validated direct PCR for use on casework bloodstains, and in 2016, the Organization of Scientific Area Committee for Forensic Science expressed a need to assess whether there is value in performing extraction and quantification on all evidence types.

Although laboratories in the United States can use direct PCR for reference samples, they are unable to implement it for forensic evidence samples due to FBI Quality Assurance Standard 9.4, which requires all unknown forensic samples to undergo human-specific DNA quantification prior to amplification of short tandem repeat (STR) loci. The goals of this presentation are to demonstrate the value and effectiveness of direct PCR for forensic DNA evidence samples and emphasize the importance of reevaluating guidelines as technologies advance and new data become available. This presentation will summarize the history of direct PCR, the advantages and disadvantages of its use for forensic DNA evidence samples, and current and ongoing research findings. Ongoing research at our laboratory involves examining direct PCR with touch DNA, including samples that have been aged for up to 6 months and samples containing PCR inhibitors.