Preanalytical Factors Influencing the Stability of Ethanol in Antemortem Blood and Urine Samples

The quantitative analysis of ethanol in blood and other biological specimens is a commonly requested service from forensic science and toxicology laboratories worldwide. The measured blood alcohol concentration (BAC) constitutes important evidence when alcohol-related crimes are investigated, such as drunken driving or drug-related sexual assault. This review article considers the importance of various preanalytical factors that might influence changes in the ethanol concentration in blood after collection and before analysis or reanalysis after various periods of storage. When blood samples were collected by venipuncture from living subjects in evacuated tubes containing sodium fluoride (NaF) preservative, there was no evidence that the BAC increased after collection. Most studies found that the BAC decreased after collection depending on storage conditions, such as time and temperature, and the amount of NaF preservative. After the storage of blood specimens in a refrigerator (4oC) for up to 1–4 weeks, the changes in the BAC were not analytically significant. After storage for up to 12 months at 4oC, under the same conditions, the BAC decreased on average by 0.01–0.02 g%. The loss of ethanol does not appear to depend on the type of evacuated tubes used (glass or plastic), nominal volume (5 mL or 10 mL) or the amount of NaF preservative. Urine alcohol concentrations were also stable after various periods of storage, although in cases of glycosuria and urinary tract and/or Candida infections, the addition of NaF (1% w/v) was essential to prevent post-sampling synthesis of ethanol.