Relation between serum and whole-blood ethanol concentrations.

An algorithm is suggested for interpretation of serum ethanol concentrations under legal statutes that specify whole-blood alcohol concentrations. The algorithm uses the distribution of individual serum:whole-blood alcohol concentration ratios to allow calculations at various levels of confidence that can be related to legal standards of evidence. Serum:whole-blood alcohol concentration ratios were determined for 211 patients. The ratios ranged from 0.88 to 1.59 (median 1.15). The distribution of ratios was positively skewed, but the logarithms of the ratios were normally distributed. This allowed the parametric calculation of a range of ratios of 0.90-1.49 for the central 99% of the population and a range of 0.95-1.40 for the central 95%. The serum:whole-blood alcohol concentration ratio was independent of both the serum alcohol concentration (R2 = 0.005) and the hematocrit (R2 = 0.03).