100284 - Tolerance to iodixanol after anaphylaxis due to iohexol, guided by Basophil Activation Test

 Immediate hypersensitivity to iodinated contrast media (ICM) is the third cause of anaphylaxis in the hospital environment, despite using lower osmolarity contrast media (better tolerated).We present a case of severe anaphylaxis to ICM where the basophil activation test (BAT) guided the selection of a safer alternative.

A 62-year-old morbidly obese woman with previous contact allergy to budesonide developed grade 2 anaphylaxis (dyspnea, stridor, tachypnea) immediately after iohexol administration during a computed tomography. Skin prick and intradermal tests (1/10 dilution) were positive for iohexol, ioversol, iobitridol and iodixanol. BAT showed positive activation only with ioversol (5.2% in 1/100 dilution), while iodixanol remained negative (3.59% in 1/10 dilution). Given the essential need for an ICM for endoscopic retrograde cholangiopancreatography (ERCP), iodixanol (dimeric, non-ionic, lower osmolarity) administration was scheduled with a premedication protocol: acetylsalicylic acid 100 mg, montelukast 10 mg, prednisone 60 mg and ebastine 20 mg daily for 3 days prior to the procedure. 

The patient underwent ERCP with 5ml of iodixanol with good tolerance and a second ERCP was performed one month later with identical premedication and again without adverse reactions. Both procedures were performed with an allergist and intensivist present.

BAT successfully identified iodixanol as the ICM with the lowest risk of reactivity in this polysensitized patient. Combined with intensive premedication, this approach allowed safe performance of necessary ERCP procedures. This case highlights the utility of BAT in guiding IMC selection when avoidance is not possible, although close monitoring remains essential given the potential for cross-reactivity between some dimeric and monomeric agents.