If a patient confirms an allergy to iodinated contrast media, my first question is "what kind of a reaction did you have when you got it?"
* Nausea/vomiting = side effect of the contrast. Some MDs premedicate just to be on the safe side.
* hives/itching/rash (immediately following injection and up to two days post injection) = mild to moderate allergic reaction: premedicate
* "my face swelled up" or lips/oral cavity edema, plus difficulty breathing = allergic reaction: premedicate
anaphylactoid reaction = speaks for itself.
Most mild or moderate reactions are indeed not reproduceable after premedication with diphenhydramine (Benadryl) and methylprednisolone (or prednisone) the day before and the morning of the exam.
Now, if the pt had an anaphylactoid reaction I would re-weigh whether the risk of doing the exam is worth the benefit of the information to be gained from the exam.
Will the course of treatment be determined by the results from the exam?
Is there another exam that may be substituted that will yield helpful information without the risk of injecting iodinated contrast?
Old-style iodine contrast agents (renografin and conray, for example) provoked significantly more allergic reactions than their newer counterparts.
These newer agents are non-ionic and low-osmolar which, while they still contain iodine
, have a history of producing fewer reactions (they seem to not activate that histamine response as readily as the old agents).
e.g.: Omnipaque and Visipaque
The simple answer to your question is no, there is no agent that is substituted (usually), however most pts who are allergic to iodinated contrast agents can receive them without sequelae if the patients are premedicated before (each hospital/imaging area has its own procedure for premeds and dosing).
(some IR [interventional radiologists] use CO2 as a contrast agent for certain exams. This isn't widely done in most places)