Plasma complement and histamine changes after intravenous administration of sodium fluorescein

Venous blood samples were obtained from 85 patients before and at three, ten, and 30 minutes after intravenous administration of sodium fluorescein. Whole complement hemolytic activity and plasma histamine were measured. The patients were observed for side effects. Clinical adverse reactions occurred in 18 (21%) of the patients. Changes in complement hemolytic activity occurred in all patients, but probably were the result of binding of fluorescein to complement proteins, or on the membrane of sensitized red blood cells used in the assay. Plasma histamine was increased within the first few minutes after infusion of fluorescein and persisted up to ten minutes. Increased histamine was found in 66% of patients with adverse reactions and in only 15% of patients with no reactions. Histamine may be an important mediator of adverse reactions to fluorescein.