Diagnostic utility of the drowning index: A review of the literature and analysis of 7105 Danish autopsy cases

BACKGROUND AND AIM: Drowning is a diagnosis of exclusion that relies on circumstantial scene- and autopsy findings. The drowning index (DI) was constructed in previous publications as a suggested aid in the diagnosis of drowning by relating lung weight to spleen weight. This study aimed to evaluate the diagnostic performance of the DI in distinguishing drowning from other causes of death associated with increased lung weight and a group of hanging deaths. METHODS: A retrospective cohort study was conducted using a database of 22,872 Danish autopsy cases, from which 7105 cases of either drowning, cardiac death, poisoning and hanging were selected. DI was calculated for each case. Descriptive statistics and group-wise comparison using Kruskal-Wallis with pairwise Wilcoxon post hoc testing, and receiver operating characteristic (ROC) analysis were performed. A literature review was conducted for comparison. RESULTS: Mean drowning index was significantly higher in drowning (n = 427) cases (15.48) compared with other causes of death (hanging: 8.89, heart failure: 10.24 and poisoning: 10.45). ROC analysis combined with Youden's index identified an optimal DI cut-off of approximately 11, corresponding to a sensitivity of 56% (CI: 51.1-60.7) and a specificity of 67.2% (CI: 66.1-68.4). Findings from the literature review were broadly comparable. CONCLUSION: In this largest study of the DI to date, we propose that the DI is best interpreted as a graded measure of evidential strength for drowning as a cause of death, rather than a dichotomous diagnostic marker.