Differentiation of heat-related deaths using quantitative evaluation of urinary myoglobin and renal tubular myoglobin deposition.

Myoglobin elevation from rhabdomyolysis is a recognized feature of heat-related deaths; however, the postmortem distribution of myoglobin across body fluids, as well as the diagnostic value of urinary myoglobin and renal tubular myoglobin deposition, remain unclear. This study aimed to characterize postmortem myoglobin distribution in multiple body fluids, assess postmortem interval (PMI) effects, and evaluate the diagnostic utility of urinary myoglobin and renal myoglobin-positive tubular casts in heat-related deaths. Myoglobin concentrations were measured in urine, serum, aqueous humor, vitreous humor, and pericardial fluid from autopsy cases. Renal myoglobin deposition was assessed immunohistochemically and semi-quantified as counts per 20 high-power fields. Associations with PMI, inter-fluids correlations, group comparisons, and receiver-operating characteristic (ROC) analyses were performed. Myoglobin concentrations varied among body fluids, with urinary levels lower than those in other compartments. Urinary myoglobin was not associated with PMI, myoglobin levels in other fluids, serum BUN, or creatinine levels, but was significantly positively correlated with renal myoglobin-positive tubular cast counts (R2 = 0.30, P < 0.0001). Urinary myoglobin levels and renal tubular myoglobin deposition were significantly higher in heat-related deaths than in non-heat-related deaths (P < 0.0001). ROC analysis showed an AUC of 0.92 for urinary myoglobin and 0.78 for renal myoglobin-positive tubular cast counts. Urinary myoglobin represents a robust postmortem marker with minimal PMI influence and limited correlation with myoglobin levels in postmortem body fluids and reflects renal tubular myoglobin deposition. Quantitative assessment of urinary myoglobin and renal myoglobin-positive tubular casts provides a useful adjunct for the postmortem diagnosis of heat-related deaths.