Dubiously Doubtful: An Exploration of the Literature Concerning Doubtful, Macular Erythema, "?+," and "+/-" Patch Test Reactions.

When the final patch test reading is barely discernable, it is termed a doubtful, macular erythema, "?+," or "+/-" reaction (hereby referred to as doubtful reaction). Information is conflicting about how to interpret doubtful reactions. Many guidelines do not comment on how to approach doubtful reactions; others state that further evaluation can (not should) be performed. In clinical reports, some investigators regard them as positive allergic reactions; some, as positive under certain circumstances; and many, as negative. Indeed, 16 (84%) of 19 recent reports of patch test reactions to standard/baseline series considered doubtful reactions negative for purposes of the report and did not include the number of these reactions. The problem is that these reactions are common and are not infrequently relevant. We recommend that researchers include frequency of doubtful reactions in reports and that doubtful reactions be assessed with the same scrutiny as stronger allergic reactions in the clinical setting.