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