Plasma level of histamine in aspirin-sensitive urticaria.

Twelve patients with a history of aspirin-induced urticaria and/or angioedema were studied before and after the provocation of symptoms with aspirin. The resting plasma histamine levels in these patients (0.95 +/- 0.25 ng/mL) were significantly higher than in 30 control subjects (0.21 +/- 0.02 ng/mL) (P less than .0005) and nine patients with non-aspirin-sensitive urticaria (0.27 +/- 0.06 ng/mL) (P less than .01). The plasma histamine levels fell significantly at the time of adverse reactions to aspirin (P less than .01). The high resting histamine levels, like the high venous prostaglandin F2 alpha levels that we have previously reported in the same group of patients and the high plasma histamine levels we have found in aspirin-sensitive asthmatics suggest an abnormality of mediator release in aspirin-sensitive patients.