Does amethocaine gel influence blood results obtained from capillary sampling?

Unlabelled: In many children routine blood samples are obtained by capillary sampling, a technique that appears to cause high levels of pain and distress in the child. Topical anaesthesia might alleviate the pain associated with capillary blood sampling but would it affect the blood sample?

Aim: a preliminary study to determine whether topical local anaesthetic would affect the values of commonly performed biochemical tests

Method: 22 healthy adult volunteers were recruited; each volunteer acted as his or her own control. Ametop was applied to a socially clean digit and covered with an occlusive dressing. After 30 minutes the dressing was taken off and excess gel was removed using a cotton wool ball. Two capillary samples were obtained from each volunteer, one from the Ametop treated digit and one from a digit on the opposing hand. The samples were analysed for sodium, potassium, glucose, urea, alkaline phosphatase (ALP), aspartate aminotransferase (AST), alinine aminotransferase (ALT) and bilirubin using a Vitros Chemistry analyser. Statistical analysis was performed on the blood results using Student's paired t-test.

Results: Sodium and potassium levels were significantly higher in the samples from digits with Ametop applied, and alkaline phosphatase was significantly lower.

Conclusion: The use of amethocaine gel (Ametop) appears to affect the results of both sodium and potassium in capillary blood samples and therefore it cannot be recommended as a suitable agent for topical anaesthesia prior to this procedure.