Contrast allergy
Formal Definition
An adverse reaction to iodinated contrast media used in CT or fluoroscopy, or gadolinium-based contrast agents used in MRI; reactions range from mild (urticaria, nausea) to severe anaphylaxis; a prior moderate or severe reaction to contrast media requires premedication with corticosteroids and antihistamines before repeat contrast administration, or use of alternative non-contrast imaging.
How It's Used on the Ward
"Contrast allergy" or "allergic to contrast" or "needs premedication" — a patient who previously reacted to contrast dye, now requiring a protocol before getting another contrast study.
Example
""Patient needs urgent CT pulmonary angiogram for suspected PE, but chart notes prior contrast reaction — hives and throat tightness after cardiac catheterization. Premedication protocol: prednisone 50mg PO at 13, 7, and 1 hour before procedure, diphenhydramine 50mg IV 1 hour before. Proceeding with contrast study given clinical urgency. Radiology and nursing aware.""
Clinical Context
Premedication protocol (elective): prednisone 50mg PO at 13h, 7h, and 1h before + diphenhydramine 50mg IV/PO 1h before. Emergency premedication (urgent study cannot wait): methylprednisolone 40mg IV q4h x3 doses + diphenhydramine 50mg IV 1h before. Seafood allergy is NOT a contraindication to iodinated contrast — the shellfish allergy myth is debunked; shellfish allergy does not predict contrast allergy. Contrast nephropathy: concern in patients with CKD (eGFR <30) — IV hydration reduces risk; hold metformin 48h after in renal disease (lactic acidosis risk). Gadolinium (MRI contrast) and nephrogenic systemic fibrosis (NSF): contraindicated with eGFR <30 for Group I agents.