Clinical value of negative skin tests to iodinated contrast media

Several studies have shown that skin tests are useful tools for the diagnosis of iodinated contrast medium (ICM) allergy, but the real number of false negative results is not known.

To evaluate the negative predictive value of ICM skin tests.

One hundred and fifty-nine patients tested in our department because of a previous ICM reaction over the last 9 years were called and asked standardized questions about ICM re-exposure.

Twenty-nine patients had been re-exposed to ICM. There were 20 (69.0%) females and the median age was 55 (34-60) years. The median time interval between the reaction and skin testing was 11.9 (1.6-21.5) years. Twenty-four patients (82%) had an immediate reaction, four a non-immediate (13.8%) reaction and no data were available for one patient. Two patients had positive ICM skin tests previously and were re-exposed to a negatively skin-tested ICM and did not react. Only two patients presented a mild reaction during ICM re-injection: one immediate (generalized urticaria lasting for 3 days) and one non-immediate maculopapular reaction. The patient with urticaria was re-tested and re-challenged (negative). The other patient was unable to return for re-testing.

Skin testing for ICM hypersensitivity has a negative predictive value of 96.6% (95% CI: 89.9-103.2) and none of the reactions in skin-test-negative patients were severe. Multi-centric large surveys are still needed for confirmation.