Abstract
With great interest I read the article by Soffer et al published in the January issue of Vascular and Endovascular Surgery. 1 The authors clearly point to the need for a predicting test in patients with a positive history of an adverse reactions against contrast media, but unfortunately they chose the wrong way. Pretesting by using intravenous injection of small doses of contrast media to possibly predict a reactivity is a very old fashioned method that has been abandoned many years ago because it has no clinical value and is harmful. 2 –5 Interestingly, while useful medical knowledge sometimes falls into oblivion, wrong facts are carried on the heritage.
Skin testing can be done with either the skin prick test or the intradermal test. By using the first option, only a very low amount of the contrast medium reaches the skin mast cells that induces in most tested patients a negative reaction and only a very small proportion of patients (with very severe clinical reactions) acquires a positive test result. Therefore, skin prick test is no useful procedure to obtain a valuable test result. As stated previously, for immediate reactors, the intradermal tests are the most sensitive, whereas delayed intradermal tests in combination with patch tests are needed for optimal sensitivity in nonimmediate or delayed reactions. 6 The intradermal test should be done with escalating concentrations of the contrast media: for example, starting with a 10−2 dilution, followed by a 10−1 dilution, and finally by the intradermal injection of the undiluted contrast medium. 7 If the patient shows a positive test result, the testing of the next concentration step should be not performed. Such a test procedure is safe and well tolerated by the patients and can be recommended as diagnostic tool both to verify the culprit contrast medium and to possible identify alternate nonculprit compounds.
A pretesting by using a small dose of a contrast medium has been inaugurated in the 1940s by Jungmichel, for example. 8 Afterward several radiologists pretested patients at risk. The evaluation of the results of the pretesting was disappointing: Pretesting has been shown to be of no clinical value, serious reactions and even deaths occurred despite negative pretesting results, and deaths and serious reactions were induced by the pretesting itself. 2 –5 Therefore, pretesting was given up. For several decades, pretesting was not performed. But with the introduction of the abovementioned skin tests, the pretesting or challenging (with or without escalating test does of the contrast medium) was reintroduced. 9 Acquisition of a sensitization has not yet been investigated, it should be the same as mentioned above.
Taken together, currently, intradermal testing up to undiluted contrast medium concentrations is the method of the choice both to verify the culprit contrast medium and to possibly find nonculprit contrast media that could be injected as safe alternate compounds. Pretesting with small volumes of the contrast medium (with or without premedication) is dangerous because it bears the risk of the acquisition of a sensitization; this means that even in negatively tested patients, reactions of all grades of severity could be possible. Therefore, pretesting with small intravenously injected doses of the contrast medium should be abandoned.