Background: The patch test procedure is frequently employed to help determine or confirm the cause of allergic contact dermatitis (ACD). The T.R.U.E. Test has become a global standard and is the commercially available patch test system currently used within the United States. Although many studies report T.R.U.E. Test data, none has measured the overall prevalence and relevance of reactions to the allergens tested by the T.R.U.E. Test. Our objective is to describe the prevalence and relevance of contact dermatitis allergens as tested by the T.R.U.E. Test.
Methods: We conducted a search of the MEDLINE database from 1966 to June 2000 for all publications on the use of the T.R.U.E. Test in the clinical evaluation of ACD in human subjects. Inclusion and exclusion criteria were applied. For each study, we identified and recorded the number of subjects tested, the number of patients with positive reactions, and the number with relevant reactions. Data were analyzed using the SAS system (Cary, NC).
Results: Ours is the first study to compile the entire corpus of published T.R.U.E. Test data and to examine these data using meta-analytic techniques. The meta-analysis shows that nickel (14.7% of tested patients), thimerosal (5.0%), cobalt (4.8%), fragrance mix (3.4%), and balsam of Peru (3.0%) are the most prevalent allergens. The 5 least prevalent allergens are paraben mix (0.5%), black rubber mix (0.6%), quaternium-15 (0.6%), quinoline mix (0.7%), and caine mix (0.7%). By contrast, North American Contact Dermatitis Data Group (NACDG) data show that the 5 most prevalent allergens are nickel (14.3%), fragrance mix (14%), neomycin (11.6%), balsam of Peru (10.4%), and thimerosal (10.4%). NACDG data indicate that the prevalence of allergy to cobalt is 9.2%. In order to assess the clinical importance of T.R.U.E. Test allergens, we employ the Significance-Prevalence Index Number (SPIN). Based on SPIN, the most clinically important allergens tested by the T.R.U.E. Test are nickel (SPIN=894), cobalt (266), fragrance mix (158), colophony (141), and thiuram mix (138).
Conclusions: Our results identify the prevalence of common contact dermatitis allergens as tested by the T.R.U.E. Test and are in general agreement with previously published reports using other patch test methods. Over 3700 allergens have been identified as causing ACD, of which the T.R.U.E. Test tests only 23. Thus, the T.R.U.E. Test is a screening test at best. Comparison with NACDG data suggests that clinically important allergens may be missed by the T.R.U.E. Test.