Estimation of half-life with confidence interval for phosphatidylethanol (PEth) in blood based on two consecutive...

BackgroundPhosphatidylethanol (PEth) is formed in erythrocyte membranes after alcohol consumption. When abstaining, the PEth level falls with a rate proportional to its concentration, and a short apparent PEth half-life supports abstinence. We here derive algorithms for calculating unbiased half-lives and confidence intervals (CIs).MethodsPEth was measured using Acquity UPC2-MS/MS systems in clinical blood samples from out-patients. We identified 6989 individuals having taken two or more PEth samples within 28 days. One measurement pair was randomly selected from everyone. We derived methods for and calculated PEth half-lives and corresponding 95% CIs for exact, rounded, and truncated data, on closed form, Monte Carlo methods and No-U-turn sampling.ResultsThe peak of the PEth half-life was at 8.62 days. Peak PEth half-life was 8.72 days for men and 8.47 days for women (P = 0.028) and on age: 8.55 days for age 18-39 years, 8.56 for age 40-59 years and 8.87 for 60+ years (P = 0.026). PEth concentration did not significantly affect half-life. CIs on a closed form performed excellently on exact data, with misclassification of abstinence for 16 out of 6989 observations (0.23%). When rounding or truncating data, misclassification occurred using Monte Carlo methods in 104 (1.5%) and 127 (1.8%) of the observations and using closed form algorithms in 855 (12.2%) and 777 (11.1%).ConclusionUnbiased PEth half-lives and CIs can be calculated and put into use in laboratory information systems. Rounding or truncating data used for PEth half-life calculation widened CIs with misinterpretations of alcohol abstinence.