Assessment of psoas muscle as an alternative matrix for postmortem toxicological screening: qualitative agreement of xenobiotic detection with femoral and cardiac Blood.

Forensic toxicology is a cornerstone of medico-legal investigations, particularly in suspected cases of poisoning. However, interpretation may be hindered by postmortem redistribution, tissue degradation, or the absence of suitable biological matrices. Indeed, in many routine forensic situations-such as massive hemorrhage, thermal injury, or advanced decomposition-blood is often unavailable or rendered unsuitable for toxicological analysis. In this context, the psoas muscle represents a promising alternative: its deep anatomical location, structural integrity, and relative resistance to postmortem change may preserve xenobiotic content and improve analytical reliability. This study assessed the qualitative agreement between psoas muscle and both femoral and cardiac blood for broad-spectrum xenobiotic detection using liquid chromatography-high-resolution mass spectrometry (LC-HRMS). Qualitative agreement was defined as the proportion of cases in which a xenobiotic detected in femoral or cardiac blood was also identified in psoas muscle. The strength of agreement between detection results in femoral or cardiac blood and psoas muscle was further evaluated using odds ratios (ORs) with 95 % confidence intervals. Sixty-four autopsy cases were included, and 78 distinct substances were identified across all matrices. Muscle samples were processed by homogenization and liquid-liquid extraction under basic conditions. The most frequently detected drugs included opioids and analgesics (n = 40), benzodiazepines (n = 27), antidepressants (n = 14), antipsychotics (n = 13), and cocaine-related compounds (n = 12). Qualitative agreement between psoas muscle and femoral blood yielded an odds ratio (OR) of 0.79; 95 % CI 0.69-0.91. Between psoas muscle and cardiac blood, the OR was 0.80; 95 % CI 0.72-0.88. These results support the analytical value of psoas muscle as a reliable alternative matrix for postmortem toxicological screening, especially for drug classes most commonly implicated in fatal poisonings. Despite some molecule-specific variations, psoas tissue may strengthen toxicological interpretation when blood is unavailable or compromised.