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Diagnostic procedures currently use prick-tests to mustard seeds or even to the condiment with similar results. The detection of allergy antibodies can easily be performed in blood samples. However as for many other foods, there is a clear discrepancy between the frequency of reactions evidenced by skin tests or blood samples, and a real food allergy. Only 23% of subjects reacting to mustard in diagnostic tests are able to react to the ingestion. Neither the size of the prick-test nor the level of allergy antibodies is predictive of a clinical reaction. Therefore, when tests are not conclusive, standardized oral challenges can be carried out in hospital settings. The diagnosis of allergy to mustard (and other spices) should be systematically considered in every case of immediate reactions after meals, where there is a strong suspicion of a food allergy, but where testing of all the common foods does not give a positive result. Also cases of unexplained anaphylaxis (so-called idiopathic anaphylaxis) could benefit from such investigations. Challenge of the lips is of no use, since there is an irritative, non specific effect of mustard on the lip. An alternative diagnosis of intolerance to sulfites has to be considered, since sulfites are commonly included in mustard seasoning itself.
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