The influence of alcohol content variation in UK packaged beers on the uncertainty of calculations using the Widmark equation

Revised equations allowing the estimation of the uncertainty associated with the Total Body Water version of the Widmark equation

Widmark calculations are the most commonly used alcohol calculations to estimate a) the amount of alcohol consumed based on blood alcohol concentration (BAC) and b) BACs at a set time after consumption of a known amount of alcohol. These calculations are vital in forensic casework. Previous work has demonstrated that using general error propagation-based equations the variability associated with alcohol calculations can be estimated, but these equations have only been determined for the volume of distribution version of the Widmark equation. However, recent investigations have shown that the total body water (TBW) version of the Widmark equation is more reliable than the version that utilizes the apparent volume of distribution of ethanol. To date, there is no general error propagation equation to determine the variability associated the TBW version of the Widmark equation. Using previously published studies of 185 individuals in which alcohol elimination rate (β) and ethanol's volume of distribution were determined, we have shown that there is a negative correlation (-0.247) between the alcohol elimination rate (β) and TBW. Using these data, we were able to produce equations allowing the estimation of the variability of the results calculated using the TBW version of the Widmark equation. This will allow forensic practitioners to give the best determination of the variability associated with Widmark calculations currently possible.

Total body water is the preferred method to use in forensic blood-alcohol calculations rather than ethanol's volume of distribution

During the prosecution and defence of drink-driving cases, forensic practitioners are often required to engage in various blood-alcohol calculations, such as whether or not the statutory limit was exceeded (e.g. 80mg/100mL, 0.08g/100mL or 0.80g/L). For this purpose, most forensic scientists utilize the Widmark equation, or some modification thereof, to calculate a person's blood alcohol concentration (BAC) based on information about the amount of ethanol consumed and the pattern of drinking. This equation comes in two main forms; one of which incorporates the apparent volume of distribution of ethanol (V) and the other a person's total body water (TBW). In this study, we utilised two independent data sets, one involving the determination of V for ethanol in 173 men and 63 women, and the other TBW determined for 582 men and 884 women. Those subjects included in the TBW group represented various racial groups (Caucasians, African Americans, Hispanics, Asians and Puerto Ricans), with body mass index (BMI) ranging from 17 to 80kg/m². Both versions of the Widmark equation were evaluated in relation to their accuracy and precision in predicting TBW and/or V using the two most common anthropometric equations; those of Watson et al. and Forrest. Both anthropometric equations exhibited good accuracy (<4.3%) for the prediction of both TBW and V. However, the root mean square error was lower TBW was used for prediction (9.09-12.84%) rather than V (11.72-15.08%). Overall, this study has demonstrated (a) that blood-alcohol calculations are more reliable using TBW rather than V (b) that both equations (Watson et al. and Forrest) are applicable to ethnic groups other than Caucasians and (c) the Forrest equation predicts TBW in men and women with BMI from 17 to 35kg/m² and that the Watson et al. equation works for those with more extreme BMI; females (17-80kg/m²) and males (17-67kg/m²).

Interpol review of toxicology 2016-2019

This review paper covers the forensic-relevant literature in toxicology from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20.Papers%202019.pdf.

Effects of alcohol consumption on copeptin levels and sodium-water homeostasis

Alcohol consumption influences sodium-water homeostasis. However, the effect of alcohol on vasopressin levels is controversial. The aim of the present study was to evaluate physiological changes of alcohol consumption on the stable vasopressin surrogate marker copeptin. In addition, we aimed at investigating the effect of additional sodium and/or water consumption on plasma sodium, osmolality, and copeptin levels. Ten healthy men underwent four interventions in random order: 1) beer consumption only, 2) beer consumption with additional water, 3) beer consumption with additional stock, or 4) water consumption only. Fluid consumption was equal between interventions and calculated to reach a blood alcohol concentration of 0.8‰ in the beer interventions. Blood and urinary samples were taken at six time points over the observation period of 720 min. The primary end point was the mean difference in copeptin levels 90 min after the start of fluid consumption, which showed no in-between group differences (P = 0.4). However, a higher total urinary volume excretion in all alcohol compared with water interventions was observed (P = 0.01). Furthermore, plasma copeptin, sodium, and urinary osmolality levels increased significantly at the end of the observation period in all alcohol compared with water-only interventions (P = 0.02). In conclusion, initial copeptin suppression does not differ between alcohol or water interventions but seems to be prolonged in the alcohol interventions. This leads to increased volume loss followed by a counterregulation with increased copeptin levels and water retention after 720 min in alcohol compared with interventions. Additional sodium and/or water consumption with alcohol did not change the observed alcohol-induced effects.

Uncertainty in Widmark calculations: ABV variation in packaged versions of the most popular beers in the UK

Forensic practitioners regularly use the Widmark equation to determine theoretical blood alcohol concentrations for use in cases involving alcohol. It is important with these calculations to determine the uncertainty associated with any result. Previous work has investigated the uncertainty in percent alcohol by volume (%ABV) from beers produced by small independent breweries in the UK but did not study the top selling beers in the UK. The top selling lagers and ales/bitters in the UK were identified by sales volume and the %ABV determined. These data was then used to determine the percent coefficient of variation (%CV) that should be used by forensic practitioners when constructing alcohol technical defence reports for use in forensic cases. These samples, from what may be described as 'big' brewers, were determined to have a smaller root mean square error (RMSE) (±0.1%v/v, n = 35), and %CV than those previously reported for beers produced by small, independent breweries in the UK. The results from this study shows that different RMSE's should be used for %ABV when determining the uncertainty of results from Widmark calculations depending if the drinks consumed have been from either 'big' brewers or small, independent breweries.