Swabbing Skin with Alcohol Could Change the Blood Alcohol Level Significantly

The standard practice before forensic blood alcohol sampling is cleaning the skin using a non-alcohol-containing swab, due to the belief that the use of an alcohol-containing swab will contaminate the sample. In their retrospective study, Miller et al. demonstrated that the use of 70% isopropyl alcohol swabs does not significantly affect blood alcohol concentration (BAC) when used before vein puncture ( ). Tucker and Trethewy confirmed this argument in their recent prospective study ( ). Although there was no significant difference in the BAC obtained with either method of skin preparation in some articles in the literature, some others reported that the levels could change with alcohol swabbing. The possible effects of the use of a dermal antiseptic on BAC testing were pointed out in Germany in 1976 ( ). Furthermore, experimental results were reported ( , , , , ). The procedures were different in each of these experiments, making direct comparisons impossible. Overall, however, it seems that contamination occurs infrequently, and that the levels are usually small when it does. In light of the experimental studies in the literature mentioned above, it can be concluded that only minute ethanol differences are produced by using alcohol-based skin-cleansing swabs and this minimal interference is unlikely to affect clinical sample results; and even in a forensic situation the inadvertent use of alcohol-based swabs is unlikely to lead to a miscarriage of justice. However, we encountered an obviously high blood alcohol level in a 20-year-old worker brought to our Emergency Department after accidentally having his head crushed under a tree trunk. His Glasgow Coma Scale score was 15 at presentation, and depressed skull fracture was suspected in the left frontal area. There were multiple lacerations at maxillary and other facial areas. Head and maxillofacial computed tomography was ordered and blood samples were taken. When the results arrived, a very high blood alcohol level—measured as 453 mg/dL—was seen. The patient was questioned again for alcohol consumption; however, he denied having ingested any alcohol. The laboratory was questioned about whether there was any problem with the test measuring method and devices; the technicians denied any such problem. When the nurse who collected the blood sample was asked about swabbing the skin, it was learned that she used an alcohol swab first and then a povidone-iodine swab before blood sampling. A new sample was collected again after povidone-iodine swabbing and the blood alcohol level was measured as 0.3 mg/dL, which was within normal limits.