Discrimination between urticaria-prone and other allergic patients by intradermal skin testing with codeine

To study the ability of cutaneous mast cells to degranulate in urticaria-prone patients, subjects were skin tested with the known mast cell degranulator, codeine sulfate. Sensitivity to codeine as determined by the concentrations of codeine necessary to cause a net wheal of 5 mm was compared between urticaria-prone subjects, allergic subjects, and normal control subjects. Urticaria-prone subjects were more sensitive to codeine at every concentration tested and exhibited a mean reactivity to codeine that was almost 100 times that of the other allergic individuals and normal control subjects. This difference could not be explained by an increased sensitivity to histamine in 71% of urticaria-prone patients nor by any dermatographic tendencies or increased relative allergic reactivity. These findings suggest that codeine skin testing can be used to identify a distinct population of patients with urticaria.