IGHE and Allergy: These patients frequently exhibit features of mast cell excess, including positive history of food and/or environmental allergies, signs and symptoms such as flushing, pruritus, tachycardia, asthma, headache, or dermatographism, and suggestive lab data such as elevated serum IgE levels or whole-blood histamine levels greater than 300 nmol/L [24, 25, 30].