Clinical Conundrums: Should I Pretreat Patients with Contrast Allergy Prior to IV Contrast Administration?

Bottom Line Up Top: Pretreatment is ineffective and unnecessary as it does not significantly reduce the risk of serious adverse reactions to contrast. Pretreatment should not delay imaging required for definitive diagnosis. 

Clinical Scenario: A 65 year-old woman presents with shortness of breath. Her vitals are notable for tachycardia and mild hypoxia, but she is otherwise hemodynamically stable. You strongly suspect a pulmonary embolism. However, the patient tells you she has a history of IV contrast allergy. Do you pretreat the patient prior to CT scan or proceed without delay and risk an allergic reaction? 

What Your Gut Says: The patient is stable and can wait 4 hours. Administer the pretreatment medications as this should prevent any severe allergic reaction.