Lymphocyte proliferation testing in chromium allergic contact dermatitis L. E. A. M. Martins, A. J. Da Silva Duarte, V. Aoki, R. S. Nunes, S. Ogusuku and V. M. S. Reis Department of Dermatology, University of Sa ˜o Paulo, Sa ˜o Paulo, Brazil Summary Background. Lymphocyte proliferation testing (LPT) has some advantages over patch testing to diagnose allergic contact dermatitis. It is harmless, objective and can be used in clinical situations where patch testing is not recommended. Unfortunately, significant success has only been achieved with nickel. There are few studies on chromium LPT and they were performed with different methods, leading to inconsistent results. Methods. To determine the best parameters for chromium LPT, we tested 20 patients with allergic contact dermatitis to the metal and 20 controls, using various protocols. Results. The best sensitivity and specificity ratios were achieved with 6-day cultures stimulated with a range from 7.5 · 10 -4 to 5 · 10 -3 mol ⁄ L of nonfiltered chromium chloride solutions. The sensitivity, specificity and accuracy values found within this range were 65%, 95% and 80%, respectively. Conclusion. Further investigation is necessary to achieve better sensitivity values. Introduction Allergic contact dermatitis (ACD), a T cell-mediated cutaneous inflammatory response to low-molecular- weight chemicals, is a common and often disabling disorder. Patch testing remains the gold standard test to confirm ACD and to identify the specific causative allergen. However, it is time-consuming, subjective and not completely safe. 1–5 The frequency and morbidity of ACD and the problems related to patch testing requires the development of an alternative test. 6 Lymphocyte proliferation testing (LPT) is an in vitro assay that evaluates lymphocyte antigen recall. Owing to its better safety profile, LPT may be used when patch testing is contraindicated. 1,7 However, good results have only been achieved with nickel, an allergen rarely associated with diagnostic difficulty. 7–9 Chromium, an elemental metal found in various oxidation states (+3 and +6), is an important cause of contact dermatitis among construction workers 10 and workers exposed to chrome-tanned leather products. 11 Hexavalent [Cr(VI)] salts are stronger allergens than trivalent [Cr(III)] compounds, partly due to the greater skin permeation of the former. 11,12 However, it has been speculated that Cr(III) is the actual hapten, as Cr(VI) is reduced to Cr(III), which in turn binds intracellular proteins, forming immunogenic com- plexes. 13 There are few studies on chromium LPT and these were performed with various protocols and scoring methods, leading to inconsistent results and doubt about its clinical applicability. 14 The aim of this study was to determine the appropriate salt, concen- tration and period of incubation for chromium LPT assay. Methods The study was approved by the local ethics commit- tee, and informed consent was obtained from all participants. Correspondence: Dr Luis Eduardo Agner Machado Martins, Francisco Rocha n 63 ap 1301 Curitiba, Parana ´ 80420-130, Brazil. E-mail:hd330@yahoo.com Conflict of interest: none declared. Accepted for publication 19 September 2007 Experimental dermatology • Original article doi: 10.1111/j.1365-2230.2008.02725.x Ó 2008 The Author(s) 472 Journal compilation Ó 2008 Blackwell Publishing Ltd • Clinical and Experimental Dermatology, 33, 472–477