Estimation of Blood Alcohol Concentrations after Social Drinking

Abstract

Requests for estimates of blood alcohol concentrations (BACs) are often made when blood samples are taken some hours after the time of interest. Many believe that such estimates are not reliable because the subject's alcohol clearance rate is never known and often there is uncertainty as to whether the subject was postabsorptive at the time in question. In order to evaluate the potential errors associated with BAC estimates under these non-ideal conditions, BAC estimates were compared with empirical data obtained from 24 healthy males, ranging in age from 22 to 56 years, who took part in a three hour social drinking session. One blood sample for alcohol analysis was taken from each subject approximately 1 hour after drinking stopped and another was taken approximately 3.5 hours after drinking stopped. Estimations of BACs at the blood sampling time points were made assuming each person had a constant blood alcohol clearance rate in the range of 10 to 20 mg/dL/h (0.01 to 0.02 g/dL/h) over the whole of the experimental period. A variety of methods were used to estimate the volume of distribution for alcohol. All BAC estimations were made assuming complete absorption and full equilibration of the total alcohol dose. The results showed that actual BACs were usually within or very close to the range of “forward” estimates based on the known alcohol doses. Furthermore, most BACs measured about an hour after cessation of drinking were within or very close to the predicted range based on back extrapolation from the actual 3.5 hour BAC result.

Alcohol metabolism of local Chinese in Hong Kong: a statistical determination on the effects of various physiological factors

“…In drunk driving cases, forensic toxicologists are often confronted with requests for providing back-calculated alcohol levels of the drivers at the time of the accident [1][2][3][4]. On many occasions, the breath or blood samples of the drivers were collected several hours after the accident, due either to the drivers leaving the scene of accident, or late arrival of law enforcement officers.…”

“…The alcohol level of breath or blood samples collected might be lower than the prescribed legal limits. In these situations, forensic toxicologists are often asked to estimate the blood alcohol concentration (BAC) of the drivers at the time of the accidents and such estimations have been known as ''back calculation'' or ''retrospective extrapolation'' [3,5,6].…”

“…Generally, a drunk driver is assumed to be in the post-absorption phase and eliminates his/her BAC level at a constant rate during the time of accident and the time that the BAC sample is collected [3,7]. The equation, C 0 = C 1 + b(t 1 À t 0 ), is adopted in back calculating the BAC level, where b is the rate of elimination, C 0 and C 1 are the blood alcohol levels at the time of accident and the time of sampling respectively, and (t 1 À t 0 ) the time lapse between the accident and blood sampling [8,9].…”

Comparison of ethanol concentrations in venous blood and end-expired breath during a controlled drinking study

“…In forensic casework, it is sometimes necessary to make forward or retrograde extrapolations of a suspect's blood-or breathalcohol concentration, e.g. from the time of sampling back to the time of driving [8][9][10]. To increase confidence in making such forensic calculations, more information is needed about the pharmacokinetics of ethanol in end-expired breath compared with venous blood.…”

Inter- and intra-subject variability in ethanol pharmacokinetic parameters: Effects of testing interval and dose

“…Stowell et al [27] supported these conclusions, finding errors in backextrapolation even over relatively short time periods when using the population average ER. Results from our study demonstrate that even if an individual specific ER, determined from a single controlled drinking experiment, is used to perform the back-extrapolation, forensically important errors are still likely to occur.…”