Patients with negative patch tests: Retrospective analysis of North American Contact Dermatitis Group (NACDG) data 2001-2016

Background: Little is known regarding the characteristics of patients with negative patch test (NPT) results. Objective: To characterize patients with NPT results. Methods: Retrospective cross-sectional analysis of 34,822 patch tested patients. NPT results were defined as negative or irritant final interpretations of all North American Contact Dermatitis Group screening allergens and no relevant allergens on supplemental series. Results: Almost one-third of patients (n = 10,888 [31.3%]) had NPT results. Patients with NPT results were significantly more likely to be male (P < .0001), be age 40 years or younger (P = .0054), be nonwhite (P = .0005), and have dermatitis primarily having a scattered generalized distribution (P = .0007) or primarily located on the lips (P = .0214) or eyelids (P = .0364). However, the absolute differences in age, race, and site were small and may not be clinically meaningful. Patients with NPT results were significantly less likely to have occupationally related skin disease (P < .0001). Overall, 8.3% of patients with NPT results had occupationally related skin disease, with precision production worker/machine operator (28.5%), health care worker (17.0%), and mechanic/repairer (7.5%) being the most commonly related occupations. In all, 22.9% of patients with NPT results had relevant irritants and 41.6% of irritants were occupationally related; cosmetics/health care products and soaps were common sources for both occupationally related and noneoccupationally related irritants. Limitations: Retrospective cross-sectional study of tertiary referral population. Conclusions: Patients with NPT results have distinct characteristics.