Problems in surveying the incidence of delayed adverse reactions to contrast media

The purpose of the study was to investigate the frequency and causative factors of symptoms unrelated to contrast media among patients who were evaluated as having late adverse reactions to non-ionic contrast media. The symptoms in both the enhanced and plain computed tomography (CT) groups were analysed. In this study the criteria for late adverse reactions were: (1) the patient had never experienced the symptoms before; (2) the symptoms had no relation to medications or orally ingested substances; (3) the symptoms occurred 1-24 h after CT scanning. Two hundred outpatients received contrast (a non-ionic, monomeric contrast media 320 mg I/ml)-enhanced CT scans and a further 200 received plain CT scans. After the CT scans were performed the patients were asked to fill out a questionnaire: 137 (68.5 %) patients in the contrast-enhanced CT group and 116 (58.0 %) in the plain CT group responded. The incidence of late adverse reactions was 7.3 % among those who responded in the contrast-enhanced CT group (Table 1) and 2.6 % among those who responded in the plain CT group, which were qualified as false late adverse reactions (Table2). The adverse events in cases 9 and 10 of Table 1 and in cases 2 and 3 of Table 2 could have been influenced by the simultaneous presence of influenza. Delayed symptoms due to factors other than contrast media include symptoms due to underlying diseases and