Effect of using alcoholic and non‐alcoholic skin cleansing swabs when sampling blood for alcohol estimation using gas chromatography

A study was carried out using 20 volunteers in whom venepuncture through the skin soaked in either ethyl or isopropyl alcohol was performed. A non-alcoholic cetrimide/chlorhexidine swab was used as a control. All subjects were initially alcohol free. Ethyl alcohol was detected in only one blood sample and the level was found to be only 0.4 mg% (roughly the limit of detection of the assay). A slightly higher level of isopropyl alcohol (3 mg%) was found in one of the blood samples. Alcohol estimation was carried out by head-space gas chromatography using a pair of instruments each fitted with a column exhibiting different retention characteristics. The system was similar to that used by other UK Forensic Science Laboratories where accurate, definitive results are a necessity. It was concluded that under very testing conditions only minute ethanol interference is produced by using alcohol-based skin cleansing swabs. 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.