Sensitivity of patch tests with rubber mixes: Results of the Information Network of Departments of Dermatology from 1990 to 1993*1

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Abstract
Mixes are used as screening patch tests. Patch tests with the single components are usually performed only in case of a positive reaction to the mix. Consequently, a mix patch test should have a high sensitivity in detecting allergies to its components. We analyzed reaction patterns of four rubber mixes and their components in the database of the Information Network of Departments of Dermatology in Germany to find if they meet this requirement. Thiuram mix has a sensitivity of .84, and mercapto mix has a sensitivity of only .57. Its component mercaptobenzothiazole indicates contact allergies to the other components with a sensitivity of .65. The test sensitivity of p-phenylenediamine mix also was rather low (.65). A patch test with N-isopropyl-N′-phenyl-p-phenylenediamine has a sensitivity of .82 for the detection of contact allergies to N-cyclohexyl-N′-phenyl-p-phenylenediamine or N,N′-diphenyl-p-phenylenediamine. Relatively few patients (n = 224) have been tested with carba mix and its components. Negative test results are reliable, but the majority of the positive test results are false positive. Thiuram mix can be recommended for a screening test. Mercapto mix should be replaced by mercaptobenzothiazole. Replacing p-phenylenediamine mix with N-isopropyl-N′-phenyl-p-phenylenediamine improves the test. In the case of carba mix, it seems better to test the three single components from the beginning.

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