Reactivity to sodium tetrachloropalladate (Na2[PdCl4]) compared to PdCl2 and NiCl2 in lymphocyte proliferation tests

Background: For patch testing, replacement of the commonly used palladium dichloride (PdCl2) by sodium tetrachloropalladate (Na-2[PdCl4]) was recently demonstrated to improve test accuracy and show a significant correlation with nickel (Ni), supporting the concept of cross-reactivity between Pd and Ni. A promising alternative to metal allergy patch testing is the in vitro lymphocyte proliferation test (LTT). Objectives: The aim of this study was to test whether Na-2[PdCl4] is also more sensitive for diagnosing Pd allergy with a standardized LTT. Patients/methods: After determining optimal nontoxic and nonmitogenic concentrations for Na-2[PdCl4], blood samples from 105 patients with clinical suspicion of metal allergy were tested with an LTT called memory lymphocyte immuno stimulation assay for Na-2[PdCl4], PdCl2 and NiCl2. Reaction profiles were analysed for concordant positive reactions. Results: Using the conventional cut-off of stimulation index >= 3, 74.3% showed a positive reaction to NiCl2, 15.2% to PdCl2 and 28.6% to Na-2[PdCl4]. All positive results to PdCl2 were covered by Na-2[PdCl4]. From the 30 positive reactions to Na-2[PdCl4], 26 (87%) were concordant for NiCl2 reactivity. Conclusion: In LTT, the use of Na-2[PdCl4] results in more positive reactions in Pd allergy testing which are in concordance with positive reactions to PdCl2 and NiCl2.