High-risk symptom histories include development of the following afterpenicillin or ß-lactam administration: anaphylaxis within 6 hours orsevere adverse cutaneous reaction (e.g., eosinophilia and systemic symptoms,Stevens-Johnson syndrome, toxic epidermal necrolysis, or acute generalizedexanthematous pustulosis) and other severe non–IgE-mediated reactions(e.g., kidney or hepatic injury, hemolytic anemia, or thrombocytopenia). This evidence concerns the gene IGHE and Increased total eosinophil count.