Theoretical and retrograde calculation of blood alcohol: wide estimates using the Academy Standards Board for calculations over an extended period of time.

Introduction: Toxicologists defend alcohol testing from their laboratories for medicolegal cases.

Methods: A 22-year-old woman drank 144.1 g of alcohol over 8.25 hours at work. Precise details of her drinking (time, volume, and alcohol content) were provided. At her shift's end, her supervisor allowed her to drive home, during which time she caused the death of another driver. Her blood alcohol concentration (BAC) was 2.20 g/L, tested a few hours later. She did not drink alcohol after her work discharge. The decedent's family sued her employer for failure to recognize intoxication. An expert was engaged to perform both theoretical and retrograde BAC estimates based on consumption and the reported BAC, respectively.

Results: Blood alcohol concentration calculations require use of the volume of distribution and the alcohol metabolism rate. The Academy Standards Board recommends reporting a range of BAC calculations. The theoretical and retrograde calculations in this case largely matched each other, suggesting that the driver did not drink after work. Due to the long interval between alcohol intake and her work dismissal, the theoretical calculation produced a wide BAC range (1.4-4.6 g/L). The retrograde calculation range was tighter (2.6-3.1 g/L).

Discussion: A prolonged duration between drinking and testing produces a range of BAC results that can cause ambiguities in legal proceedings.