Summary. The aim of this study was to examine whether the time of observation of patch tests results may have influence on the final interpretation of these results. For this purpose, a group of 188 contact dermatitis patients was patch tested. In 13 patients the results of interepretation after 48 hours differed for one or more tested substances, from the readings after 72 and 96 hours. It is concluded that skin reaction should be checked also 72 and 96 hours after the beginning of the patch test procedure in order to avoid possible misinterpretations.
Key words: contact dermatitis, delayed type skin allergy, diagnostics, patch tests, methodology.
Some dermatologists assess the skin reaction on test areas only after 48 hours while performing patch tests. This does not to be in line with the knowledge about delayed hypersensitivity. Therefore, I decided to do this study to ensure myself if it was enough to assess the patient's reactivity to the tested substance during 48-hr observation. The present study has shown that the 48-hour period is not enough to get appropriate picture of patient's contact dermatitis, because a misinterpretation of test results may occur in 3.5 - 10.5 % of patients if tests are read only at this time point.
188 patients (134 female and 54 male, aged 19 - 62 years) with contact dermatitis were tested in order to find the causative agent. The test kits "Standard I", "Standard II", "Rubbers", "Resins", "Cosmetics" and "External Drugs" were purchased from the E. Jaworski Company (Katowice, Poland). The test substances were applied onto patches of filter paper of 1 x 1 cm. Then, the patches were placed on the skin and fixed using hypoallergenic adhesive tapes. After 48 hours the tapes were removed and the skin reaction was observed. Next the removal of the patches with allergens and first observation followed. The second assessment was made in 72nd and in 96th hours after starting the test. The results were recorded using the following interpretation scheme: - negative reaction, ? doubtful reaction (light redness on the contact area), + weak (erythematous only) reaction, ++ strong (oedematous or vesicular) reaction, +++ extreme (bullous or ulcerative) reaction.
In 13 patients, the results of interpretation carried out after 48 hours differed, in the case of at least one tested substance, from the interpretation results after 72 and 96 hours. They amount to 6.9% of the observed group, with the 95%-confidence interval ranging from 3.3-10.5 %. The detailed data regarding these 13 patients are shown in Table 1.
|48 h||72 h||96 h|
Interpretation of patch tests results based upon the skin reaction after 48 hours only may lead to misinterpretation at least by one test substance in 3.5 to 10.5 % of patients tested. Therefore, the skin reaction should be checked also 72 and 96 hours after the beginning of the patch test procedure.
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