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May 20, 2011

Patients with Iodine or Seafood Allergy CAN Receive Contrast During CT Scans

It is a prevalent belief out in the medical (and lay public) community that patients with iodine or seafood allergy can not receive contrast when undergoing certain radiological tests like CT or MRI scans. The concern is that contrast contains minute amounts of free iodide and as such, IV administration of this material puts the patient at risk of a life-threatening anaphylactic reaction.

Contrast is often given in these tests as it traces out bloodflow enabling the physician to see organ and mass architecture much more clearly allowing for improved accuracy in seeing anything abnormal.

Well... rest assured that patients with iodine and seafood allergy CAN receive contrast without any significant increased risk of an allergic reaction as compared to other allergies.

In a large study encompassing 112,003 patients, only 5% had a reaction. The relative risk of a reaction in patients with seafood allergy was 3.0 compared with 2.9 for those with allergy to eggs, milk, or chocolate; 2.6 for those with allergy to fruit and strawberries; and 2.2 for those with asthma [7]. In other words, a seafood allergy increases the risk of a contrast reaction by about the same factor as does any other allergy. At least 85% of patients with seafood allergy receiving IV contrast material will not have an adverse reaction.

Formation of potential antigens from radiographic contrast media. Acta Radiol 1987; 28:473-77
Immunologic basis for adverse reactions to radiographic contrast media. Acta Radial 1990; 31:605-612
Contrast media reactions: experimental evidence against the allergy theory. Br J Radiol 1984;57: 469-173
Adverse reactions to intravascularly administered contrast media. AJR 1975;24: 145-152

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