Large-scale reanalysis of refrigerated antemortem blood samples for ethanol content at random intervals.

Ethanol stability in antemortem blood stored under various conditions has been widely studied. Most such studies have somewhat limited sample size (<50) and limited variation in the length of time between the blood draw and the first analysis and between the first analysis and the reanalysis. In the work presented here, the antemortem blood drawn for forensic purposes and stored refrigerated (~4°C) in 371 cases was analyzed for ethanol concentration using headspace gas chromatography at various times after the blood draw based on routine case flow and then also analyzed at various times within approximately 1 year after the first analysis. This methodology is intended to provide insight into the range of differences expected when cases are analyzed in the normal flow of casework and then reanalyzed at random times afterwards as occurs when reanalysis is performed by the defense or by the laboratory if the original analyst is unavailable to testify. In 22 cases, the same blood tube from the case was reanalyzed. The previously unopened blood tube from the case was analyzed in 349 cases. The 25 cases in which the blood was ethanol-negative based on the first analysis remained ethanol-negative when reanalyzed. The average difference in ethanol concentration between tests for the ethanol-positive cases was -0.004 g/dL. This decrease was statistically significant at the 0.05 level of significance. The range of differences was -0.0197 to 0.0103 g/dL. The difference measured in 85% of the ethanol-positive cases was in in the range of -0.008 to -0.001 g/dL.