Postmortem bioelectrical impedance analysis: Exploratory Assessment of phase angle behavior across different postmortem intervals

The estimation of the postmortem interval (PMI) remains a major challenge in forensic practice, particularly beyond the early postmortem phase. Bioelectrical Impedance Analysis (BIA) is a non-invasive technique widely used in clinical medicine to assess tissue electrical properties, but its application in forensic thanatochronology is still limited. This pilot study aimed to evaluate the feasibility of postmortem BIA and to investigate the relationship between PMI, body mass index (BMI), and bioelectrical parameters in a series of human cadavers. BIA measurements were performed in 29 deceased individuals using a single-frequency analyzer, recording resistance, reactance, impedance, and phase angle. The postmortem interval ranged from 1.60 to 192.87 h. Thirteen cases underwent forensic autopsy, and in ten of these subjects BIA measurements were repeated after autopsy to assess the impact of invasive procedures. Associations between PMI, BMI, and bioelectrical variables were explored using correlation analysis and exploratory regression modeling. Among the evaluated parameters, phase angle showed a moderate positive correlation with PMI (r = + 0.46), showing a tendency toward higher values with increasing postmortem interval. Reactance demonstrated a weak positive correlation with PMI (r = + 0.25), whereas resistance and impedance showed no meaningful association with postmortem time. No significant correlation was observed between BMI and PMI. Exploratory regression analysis indicated that the temporal behavior of phase angle was better described by a log-linear model than by a simple linear relationship, although substantial inter-individual variability remained. In all cases with paired measurements, phase angle values increased after autopsy, suggesting a systematic effect of anatomical disruption and fluid redistribution. These findings demonstrate that BIA is technically applicable in the postmortem setting and that phase angle exhibited measurable but highly variable time-related changes after death. However, the influence of autopsy procedures and the magnitude of residual variability indicate that phase angle may provide limited supplementary temporal information but cannot currently be considered a reliable PMI estimation tool. Further studies with larger cohorts and standardized protocols are required to clarify its forensic applicability.