Can expired TRUE Test® be used for patch testing?

Abstract

Patch testing is a method for diagnosing allergic contact dermatitis, and the best way to differentiate it from irritant contact dermatitis (1). As part of the Spanish Contact Dermatitis Society baseline series, the thin-layer rapiduse epicutaneous test, known as TRUE Test® (TT), is widely used (2–4). With the aim of studying the diagnostic capacity of expired TRUE Test® panels, a prospective study on consecutive patients attending our occupational dermatology department during February 2013 was conducted. In all patients, three TRUE Tests® with different expiry dates (2011, 2012, and 2013) were applied. Also, according to the clinical history and occupation of each patient, patch testing with a specific series was performed. Patients signed an informed consent form before the study was performed. The patches were removed on D2, and readings were performed on D2 and D3. During the study period, a total of 11 patients were patch tested with three TRUE Tests® with different expiry dates: 2011, 2012, and 2013. In 9 of 11 patients, the same positive reactions, with identical intensities, were observed in the three TRUE Tests® (Fig. 1). In the remaining 2 patients, the same positive reactions were observed in the TRUE Tests® with expiry dates in 2012–2013, and negative results were obtained in the TRUE Test® in with an expiry date in 2011 (Table 1).