Improving povidone-iodine and iodine preparations for patch testing

Background Allergy evaluation by patch testing with povidone-iodine (PVP-I) or iodine remains challenging, because current patch test preparations frequently lead to false-positive or irritant skin reactions. Objectives To investigate different preparations for iodine patch tests and to assess their clinical relevance with repeated open application tests (ROATs). Methods We monocentrically analyzed 95 patients with suspected allergy to disinfectants in retrospect who underwent parallel iodine patch testing with four preparations: PVP-I 2% aq., 5% aq., 10% aq., and iodine 0.5% pet. Results In 27 of 95 patients (28.4%), we found positive reactions to one of the four test preparations. After ROATs in 22 of these 27 positively tested individuals, only one patient was diagnosed with iodine allergy. In contrast, 31 of 95 patients (32.6%) showed irritant or questionable patch-test reactions on day 2 (D2) and/or D3 and/or D7 to one or more test preparations. Testing with PVP-I 2% aq. resulted in the lowest number of doubtful skin reactions while detecting the single allergic patient. Conclusion PVP-I 2% aq. was found to be the optimal patch-test preparation. In general, iodine allergy appears to be substantially overestimated, and positive patch test responses to iodine should prompt an urgent ROAT for confirmation before diagnosing iodine allergy.

Automated summary

Patch testing with PVP-I 2% aq. showed the lowest number of doubtful skin reactions while detecting the single allergic patient, suggesting it as the optimal preparation for iodine patch tests. Overestimation of iodine allergy was indicated, and positive patch test responses to iodine should be confirmed with ROATs before diagnosis.