Thanatochemistry and the role of hypoxanthine in the post-mortem interval estimation: a systematic literature review

The estimation of post-mortem interval (PMI) is of utmost importance for forensic pathologists due to its implication in medico-legal evaluations. Research over the last thirty years has sought new methods for estimating the time of death, particularly focused on human biomarkers whose concentration changes over time after death. Although most studies are based on potassium (K⁺) concentrations in blood and vitreous humor (VH), hypoxanthine (Hx) has shown great promise in assessing PMI. Following PRISMA guidelines, this systematic review addresses the PICO question: "In human cadavers, what is the role of hypoxanthine, where, and with what analytical techniques is it currently used for post-mortem interval estimation?". Twenty-four papers were retrieved. The results indicate that Hx concentration can be estimated in various biofluids, VH being the most commonly accounted for. Furthermore, different pre-analytical procedures are resorted to for sample preparation, such as several methodologies utilized to detect Hx concentration. The relationship between the so-obtained Hx levels and PMI is expressed quantitively (through regressions or correlation coefficients) or semi-quantitatively (by changes in nuclear magnetic resonance spectra). PMI estimation accuracy improves significantly when additional factors are considered (such as ambient and rectal temperature, urea concentration, body weight, and cause of death) or when new methodologies providing flexible regression models are applied. Despite the promising potential, many limitations remain. Notably, the heterogeneity of sample selection and pre-analytical/analytical phases leads to inconsistent results. Thus, much more should be done to lay procedural standards and optimize biochemistry and Hx utilization in PMI-related forensic investigations.