Lack of effect on blood alcohol level of swabbing venepuncture sites with 70% isopropyl alcohol.

OBJECTIVE

It is standard practice to clean the skin using a non-alcohol-containing swab before forensic blood alcohol sampling, because of the belief that the use of an alcohol-containing swab will contaminate the sample. The present study aimed to determine whether cleaning the skin with 70% isopropyl alcohol swabs, before venepuncture, alters measured blood alcohol level (BAL).

METHODS

Volunteers aged >18 years had paired venous blood tests, which were drawn within 2 min of each other. One arm was swabbed with a 70% isopropyl alcohol swab and allowed to dry before venepuncture. The other was swabbed with saline, and these concurrent samples were used as controls. BAL was tested using the enzymatic method. Pathologists analysing the samples were blinded to the swabbing technique used. The mean differences and standard deviations of each of the paired samples were analysed using Student's t-test.

RESULTS

Fifty-six paired venous blood samples were obtained from volunteers. Mean BAL in the isopropyl alcohol-swabbed group was 3.27 mg/dL with a standard deviation of 1.14 mg/dL. Mean BAL in the saline-swabbed group was 3.41 mg/dL with a standard deviation of 1.11 mg/dL. The mean difference was 0.14 mg/dL, with a standard error of 0.157. There was no statistically significant difference between the groups.

CONCLUSIONS

The present study demonstrated that the use of 70% isopropyl alcohol swabs does not significantly affect BAL when used before venepuncture. This has implications that challenge current forensic blood alcohol sample acquisition.