Comparison of Ethanol Concentrations in Blood, Serum, and Blood Cells for Forensic Application*

Ethanol concentrations in serum (SAC) and whole blood (BAC) were determined for 235 subjects by a headspace gas chromatographic method. The SAC:BAC ratios ranged between 1.04 and 1.26. The mean was 1.14, and the normal distribution had a standard deviation (SD) of 0.041. When a conversion (division) factor for SAC to BAC of 1.18 (mean + 1 SD) was used, 84% of estimated BACs were less than that measured; the remaining estimates differed by less than 7 mg/dL. An SAC greater than 100 mg/dL reliably indicated a BAC of more than 80 mg/dL. Ethanol concentrations in blood cells (CAC) were similarly determined for 167 of these subjects. The CAC:BAC ratios ranged from 0.66 to 1.00 and had a mean of 0.865 and a negatively skewed normal distribution with an SD of 0.065. When a conversion (division) factor for CAC to BAC of 0.93 (mean + 1 SD) was used, 89% of estimated BACs were less than that measured; the remaining estimates differed by less than 8 mg/dL. A CAC greater than 80 mg/dL reliably indicated a BAC of more than 80 mg/dL. The CAC is useful in forensic practice when either blood or serum is not available.