Guidelines for estimating the amount of alcohol consumed from a single measurement of blood alcohol concentration: re-evaluation of Widmark's equation.

This article deals with the pharmacokinetics of ethanol and the reliability of estimating the amount of alcohol ingested from a single measurement of a person's blood alcohol concentration (BAC). Blood alcohol curves were plotted for 108 male subjects after they drank various doses of ethanol (0.51-0.85 g/kg body weight). The rate of disappearance of ethanol from the blood (beta-slope) and the apparent volume of distribution of ethanol (Widmark's rho factor, rho) were calculated for each subject; the mean beta-slope was 13.3 mg/dl/h (SD = 2.0), and the mean rho factor was 0.689 l/kg (SD = 0.061). The value of beta increased slightly with increasing dose of alcohol (P < 0.05). The blood alcohol parameters beta and rho were negatively correlated (r = -0.135). The BACs measured at 2 h and 5 h post-drinking were used to estimate the amount of alcohol each subject had consumed according to the method proposed by Widmark [1]. The mean differences (estimated-actual) and the +/- 95% limits of agreement were -0.72 g (+/- 12), and 2.2 (+/- 15), for the 2 h and 5 h BAC values, respectively. A method based on error propagation was used to derive the 95% limits of uncertainty in the amount of alcohol ingested. On the basis of a single measurement of BAC, we could estimate the amount of alcohol ingested within +/- 20%.