CD63 and anaphylaxis: Skin tests, which involve exposure of the mast cells in the skin of patients who experience anaphylaxis to the suspected allergen, remain the gold standard for detection of IgE‐mediated reactions.27 The optimal time for testing is generally considered to be 3–4 weeks after an acute anaphylactic episode.31 The allergist undertaking the relevant tests must be experienced in the management of drug allergies.26 Additionally, during anaphylaxis, proteins such as CD63 and CD203c become newly or increasingly expressed on the surface of basophils.