Insulin-induced drug eruptions and reliability of skin tests

Allergic reaction to insulin preparations seemed to have decreased since the introduction of contaminant-free, human preparations. The role of protamine sulfate in decreasing the prevalence of allergy is unclear. This study examines the causative components of insulin allergy along with the value of skin tests for diagnosis. Eleven patients with insulin allergy and 53 patients receiving insulin but without an insulin allergy were included as controls. Intradermal skin tests were conducted using preparations containing various concentrations of insulin [Neutral protamine Hagedorn (NPH) insulin, regular insulin (RI)] and protamine sulfate. Of the 11 patients studied, 3 had anaphylaxis and 8 displayed localized reactions. All of the patients reacted positively during skin testing. Five patients showed positive intradermal skin test reactions to protamine sulfate, and 4 reacted to insulin. Two patients that were not tested with protamine sulfate reacted positively to NPH insulin. In the case of protamine sulfate, 4 patients with localized symptoms displayed positive reactions at concentrations of 10 microg/ml, 3 microg/ml or 0.3 microg/ml. One patient with anaphylaxis reacted positively to a concentration as low as 0.03 ng/ml. In the case of insulin protein, 3 patients reacted positively to a 100-fold dilution (1 UI/ml). Eight of the 53 controls experienced pruritus and/or skin lesions. However, none of the controls reacted at a concentration of NPH insulin of less than 10 U/ml or to protamine sulfate at less than 30 microg/ml. Allergic reactions to protamine sulfate are common and should not be ignored. This study shows a good correlation between clinical manifestations and skin test reactions for insulin allergy.