Skin test and use of side chain for LOCM classification
Skin testing was performed with seven LOCMs (iobitridol, iohexol, iomeprol, iopamidol, iopromide, ioversol, and iodixanol) to evaluate cross-reactivity among LOCMs and determine potentially safer alternative LOCMs. The skin prick test (SPT) was performed with undiluted LOCM and the intradermal test (IDT) was performed with a 1:10 diluted solution. SPT was considered positive if the size of the wheal was at least 3 mm in diameter or at least 2 mm with erythema after 15 minutes. IDT was considered positive if the size of the initial wheal after injection of 0.05 mL of LOCM increased at least 3 mm in diameter or 2 mm in diameter with erythema after 20 minutes. To assess the cross-reactivity between two LOCMs, the co-positivity rate of each pairs was calculated as the percentage of cases in the intersection area that showed positivity to both LOCMs.
We classified the LOCMs based on their sharing of N-(2,3-dihydroxypropyl) carbamoyl side chains (Supplement A). Iodixanol, ioversol, iopromide, iomeprol, and iohexol contain the identical common side chain while iopamidol and iobitridol do not. This classification was based on a recent study which designated iopamidol as a group without sharing the identical N-(2,3-dihydroxypropyl) carbamoyl side chain because of its subtle difference from others.19