Patch test reactions at D4, D5 and D6

In this retrospective study, patch test reactions in 3 groups of patients w ere analysed, in order to obtain information on the best day for the 2nd pa tch-test reading after day 2 (D2), on the usefulness of additional readings after D3, and on the dependence of patch-test reactions at D4, D5, or D6 o n allergen and/or patient characteristics. In the years 1990 to 1995, patch tests were routinely read at D3 and D4 in 1096 patients, at D3 and D5 in 1 243 patients, and at D3 and D6 in 1136 patients. In all of the 3 groups, si gnificantly more positive reactions diminished than appeared de novo from D 3 to the later reading. Virtually identical results were observed in subgro ups of patients formed by sex, age or atopy. However, men might possibly re act more slowly than women on patch testing, showing more increasing than d iminishing reactions in the D3/D4- and the D3/D5-comparison. Reactions to i ndividual allergens showed wide differences in this connection. Neomycin su lfate, cobalt salts, and p-phenylenediamine can be characterized as slow al lergens, with more reactions increasing than diminishing from D3 to the lat er readings. With fragrance mix and balsam of Peru, the opposite pattern oc curred. In all subgroups of patients, and with most allergens, the gain in positive reactions was biggest when an additional reading was performed at D5. We conclude that for a single 2nd patch test reading after D2, D3 is th e best day, and especially better than D4. If a 3rd reading is performed, i t should be done at D5 to get the maximum information out of patch testing. However, this extends the test procedure to at least 1 day of the weekend.