Intradermal compared with prick testing in the diagnosis of anaesthetic allergy

We have tested the hypothesis that intradermal testing is a more effective method for determining the drug responsible for anaesthetic anaphylactic reactions than prick testing in 212 consecutive patients, aged more than 10 yr, referred to an anaesthetic allergy clinic over a 4-yr period. The study was a prospective, non-randomized design. Intradermal testing was conducted using a previously described method and diluted drugs, and prick testing using undiluted drugs (with the exception of opioid analgesics which were diluted 1:10). The tests were performed on individual patients' forearms on the same occasion. Patients were followed-up to determine the results of subsequent anaesthesia and the difference between tests was analysed using kappa and tau statistics. There was 93% agreement overall between the paired tests. Which test detected the drug responsible was dependent on diagnostic criteria for positivity. The differences between the tests were not statistically significant. Using both tests improved predictability by 67% (tau=0.67, P<0.001). We conclude that in the absence of data to support one test being superior, other factors influence the choice of test. Prick testing was cheaper, and the reduction in pain and trauma with prick testing makes it more suitable for children. However, there are no data available on the safety of subsequent anaesthesia based on the results of prick testing alone, and reliability with time has not been assessed. Intradermal testing may be easier for the infrequent user. Skin testing is valuable in the investigation of anaesthetic anaphylaxis whichever test is chosen. When there is doubt both tests should be performed.