A Height-Normalised Revised Drowning Index for Thoracic Fluid Burden: Associations with Water Type, Sex, Toxicology...

Background: The forensic diagnosis of drowning lacks pathognomonic signs, and visceral weight-based indices normalised to spleen or heart weight have shown variable discriminant performance. We assessed a height-normalised revised Drowning Index (rDI) as a measure of thoracic fluid burden in confirmed drowning cases, not as a case-control test of drowning versus non-drowning deaths. Methods: Fifty-five institutional drowning cases (Ancona and Turin Province, Italy, 2008-2020) were analysed. The rDI and the original spleen-normalised Drowning Index (DI) were calculated. A multivariable linear regression assessed sex, water type, and toxicological status as simultaneous covariates; a receiver operating characteristic (ROC) analysis evaluated the within-cohort classification of water type; and the associations with the postmortem interval (PMI) were explored separately. Results: The rDI was independently associated with the male sex (standardised β = 0.391, p = 0.002) and saltwater drowning (β = 0.331, p = 0.011; adjusted R² = 0.269). The three benzodiazepine-positive institutional cases had a lower rDI in the univariate analysis (p = 0.019), but the association was not retained in the multivariable model or in a freshwater-restricted sensitivity analysis. Alcohol exposure showed no association. The water-type ROC analysis yielded an area under the curve of 0.727 (95% CI 0.553-0.871); the distributions overlapped substantially. The original DI was not associated with the variables studied. The rDI showed no significant association with the PMI within the range represented by all but one case (1-12 days). Conclusions: The rDI quantified the variation in the thoracic fluid burden within this cohort of confirmed drownings and showed moderate, exploratory water-type classification. It is not a stand-alone diagnostic test, and its discrimination ability between drowning and non-drowning deaths was not assessed. Dedicated case-control and external validation studies are required before forensic cut-offs can be recommended.