Pre-analytical Associated Factors of Foreign DNA Detection Beneath Deceased’s Fingernails

Abstract

Objective: To assess the pre-analytical factors including hand-side, representative collection technique and individual forensic physician for foreign deoxyribonucleic acid (DNA) detection in specimen collected from deceased’s fingernails. Material and Methods: This cross-sectional study, of an initial 164 samples from the fingernails of both hands, of 82 deceased caseworks; from 2010 to 2018, at the Forensic Unit, Faculty of Medicine, Prince of Songkla University. The autosomal short tandem repeats profile fingernail DNA results, pre-analytical factors, and the deceased’s characteristics were obtained from the records. The fingernail DNA outcomes were evaluated and ranked into five groups, i.e., high-level profile, low-level profile, or residual profile; if foreign alleles of more than 11 alleles, 4 to 11 alleles, or less than 4 alleles were detected, respectively. The non-specific profile group consisted of foreign DNA being detected; however the peak signals were below the decisional threshold. The unidentified group consisted of no foreign DNA being detected. The full model underwent both directional stepwise model selection, and the resulting model with the lowest Akaike information criterion was selected as the final model. The final model was analyzed by ordinal logistic regression for significant associated factors: at a 95% confidence level. Results: The representative collection technique is an associated factor, via the use of fingernail swabs (adjusted odds ratio (ORa)=13.44, 95% confidence interval (CI)=2.89–62.45), and had a larger effect size than using fingernail cuttings (ORa=6.84, 95% CI=1.47–31.86). Conclusion: At post-mortem examination, for the collection of foreign DNA from fingernails, the use of fingernail swabs, as a collection technique, is of particular interest.