Patch testing in Hong Kong

The acceptability and value of patch testing in Hong Kong was studied in 56 cases of suspected dermatitis (CD), 26 cases of endogenous eczema (EE) and 30 cases of unclassified eczema (UE), selected systematically: all those suspected of having CD and 1 in 3 of the others. 81.3% of the 112 patients selected accepted the test. The main reasons for refusal were inconvenience and lack of time for the readings. Of the 91 tested, in 88 they were successfully completed. In 39 patients, the results were negative, while 49 patients reacted to 1 or more allergens. The 2 commonest sensitizers were fragrance–mix (15 patients) and nickel sulphate (14 patients). The “usefulness” of patch testing was defined as it causing the initial clinical diagnosis to be changed. The test was found to be “useful” in 10 cases (21.3%) of those diagnosed as CD in 2 respects: (a) changing the diagnosis from irritant to allergic CD (6 cases) and (b) changing the diagnosis from CD to a suspected substance, to CD to another unsuspected substance (4 cases). For EE and UE, the initial diagnosis was changed to allergic CD in 3 (18.7%) and 7 (28.0%) cases, respectively.