The reproducibility of patch tests

Abstract

There is conflicting evidence regarding the reproducibility of patch testing. Discordant results have been reported in up to 44% of cases. The clinical relevance of these discordant patch tests has not been previously assessed. We studied 383 consecutive patients receiving simultaneous duplicate patch testing on opposite sides of the upper back with 10 allergens from the European standard series. Completely discordant patch tests-a negative test on one side with a positive test on the opposite side-were recorded in 30 (8%) patients. Two patients had discordant tests to two of the allergens; 28 had discordant reactions to one allergen. Completely discordant tests were recorded for nickel in 10 (3%) patients, balsam of Peru in two (0.5%), thiomersal in one (0.3%), cobalt in four (1%), paraphenylenediamine in three (0.8%), fragrance mix in two (0.5%), formaldehyde in four (1%), potassium dichromate in two (0.5%), lanolin in three (0.8%) and Kathon CG in one (0.3%). Of those patients with completely discordant patch tests, the allergen was deemed to be a true positive in 11 (3% of total) cases and of possible relevance in a further three. The allergen was felt to be relevant to the presenting complaint in seven (2% of total) patients.

Evaluation of a Self-Test Device Used in Allergic Contact Dermatitis

“…In a comparative study in which TRUE Test allergens were used on both sides of the back, 5% of the nickel and 10% of the fragrance-mix reactions were positive-discordant, i.e. positive only on 1 side of the back [14] ; again, this was higher than what was reported for petrolatum-based tests [15] .…”

Nickel Elicits Concomitant and Correlated in vitro Production of Th1‐, Th2‐Type and Regulatory Cytokines in Subjects with Contact Allergy to Nickel

“…In vitro testing could potentially be used as a diagnostic tool for a panel of contact allergens and offers several advantages in comparison with patch testing [21,22]. From the patients' point of view, in vitro testing only requires a blood sample whereas patch testing involves exposure to the potential allergens and several visits to the clinic.…”

“…The present diagnosis of ACD relies on the patch test, where a series of the most common contact allergens, including Ni 2þ , are applied epicutaneously on the back for several days followed by a grading of a possible reaction [20]. The patch test has a number of pitfalls which include variable results [21,22] and subjective interpretation and thus occurrence of false-positive and false-negative reactions [20]. A number of studies have been carried out aimed at developing in vitro assays to replace or complement the patch test.…”

Allergic contact dermatitis from polyethylene glycol monomethyl ether 350 in Solaraze® gel

“…Such discordance is hard to explain but is, more generally, a well‐recognized phenomenon. Bourke et al (15) noted discordant results on opposite sides of the back in 30 of 383 patients (8%) patch tested.…”