Frequency and diagnostic findings of type I and type IV reactions to beta‐lactam antibiotics – significance of the time interval between clinical reaction and skin testing

27/116 (23%) patients reacted in the skin tests. Type I sensitizations were detected in 4/35 patients (11%), type IV sensitizations in 23/83 (28%). In the case of negative in vitro diagnostics and skin testing, inpatient provocation tests were performed in 41/89 (46%). Type I allergies were confirmed in two of the 13 provoked patients (15%) with immediate type reactions, type IV allergies in three of 29 (10%) with delayed type reactions. The results were clearly related to the time interval after reaction. At less than one year, 19% (22/116) reacted, whereas only 4% (5/116) reacted at more than one year (for type I reaction 9% vs. 3%; for type IV reaction 23% vs. 5%). CONCLUSIONS: The importance of the time interval between clinical event and allergological testing supports the guideline recommendation for skin testing within one year. Guideline recommendations on the diagnostic procedure for unclear reactions that occurred in the more distant past are desirable in order to rule out allergies to beta-lactam antibiotics.