Efficacy of intravenous pretesting and antihistamine prophylaxis in radiocontrast media--sensitive patients.

Intravenous pretesting with radiocontrast media (RCM) was performed in 204 RCM-sensitive patients considered for repeat contrast radiography. Group 1 had vague histories of prior anaphylactoid reaction and negative pretests, and 2 of 41 (4.9%) had reactions upon contrast radiography. Groups 2 to 5 had definite histories of prior anaphylactoid reaction. Group 2 had the radiographic study cancelled: 18 of 21 (85.7%) had positive pretests. Group 3 had positive pretests and underwent contrast radiography, and 9 of 15 (60%) had reactions despite premedication. Group 4 (no premedication) and group 5 (diphenhydramine premedication) had negative pretests, but 11 of 53 (20.7%) and 3 of 71 (4.2%), respectively, developed reactions (p less than 0.001). The reaction frequency in group 3 (posivie pretest) of 12 of 18 (66.7%) was greater than that in groups 4 and 5 (negative pretest) combined (14 of 124 (11.3%), p less than 0.001). Intravenous pretesting identified a high-risk group and diphenhydramine premedication decreased the frequency of reaction in patients sensitive to radiocontrast media.