Using total RNA quality metrics for time since deposition estimates in degrading bloodstains

Abstract

Determining the age, or time since deposition (TSD), of bloodstains would provide forensic scientists with critical information regarding the timeline of the events of bloodshed during a crime. The physicochemical changes that occur to major biomolecules as a bloodstain dries can be used to estimate the TSD of bloodstains. For example, high-resolution automated gel electrophoresis can be used to quantify the timewise degradation of DNA present in bloodstains. Our study aims to analyze and quantify the timewise degradation trends found in total RNA from bloodstains, expanding the scope of the TSD research which has previously explored DNA and targeted mRNA molecules. Fifty bloodstains were stored in plastic microcentrifuge tubes at room temperature and tested over 10 different timepoints spanning one week. A total of eight RNA metrics were visually assessed and quantified using linear regression. RNA Integrity Number equivalent (RINe), total RNA concentration, and 28S/18S rRNA peak area ratios were retained for further analyses based on their relationship with time and limited correlations. RINe and total RNA concentration both exhibited negative trends over time, highlighting a decrease in quality and quantity. RINe was the RNA metric that demonstrated the greatest association with time (R2 = 0.696). Generalized linear mixed-effects models including donor (biological replicate) as a random effect increased the fit for all RNA metrics to varying degrees, but no significant differences were found between biological replicates for the RINe metric. Our results illustrated the presence of a significant decrease in the retained RNA metrics after 24 hours, suggesting that this method could be used to reliably differentiate day-old bloodstains from older bloodstains. Future work should focus on recreating this study in different environmental conditions, including testing on a variety of substrates.