Relative blood loss in forensic medicine—do we need a change in doctrine?

In forensic medicine, blood loss is encountered frequently, either as a cause of death or as a contributing factor. Here, risk to life and lethality assessment is based on the concept of relative blood loss (absolute loss out of total volume). In emergency medicine, the Advanced Trauma Life Support (ATLSⓇ) classification also refers to relative blood loss. We tested the validity of relative blood loss benchmarks with reference to lethality. Depending on the quality of the total blood volume (TBV) estimation formula, relative blood loss rates should be reflected in the case cohort as significantly higher absolute blood loss in heavier individuals since all TBV estimation formulas positively correlate body weight with TBV. Method: 80 autopsy cases with sudden, quantifiable, exclusively internal blood loss were retrospectively analyzed and a total of 8 different formulas for TBV estimation were applied. Results: No statistical correlation between body weight and absolute blood loss was found for any of the tested TBV estimation algorithms. All cases showed a wide spread of both absolute and relative blood loss. Discussion: The principle of relative blood loss is of very limited use in casework. It opens the forensic expert opinion to unnecessary criticism and possible negative legal implications. Conclusion: We challenge the use of relative blood loss benchmarks in textbooks and practical casework and advocate for its elimination from the ATLSⓇ ’s grading system. If necessary, we recommend the use of BMI-adjusted algorithms for TBV estimation.