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 (Na₂[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 Na₂[PdCl₄] is also more sensitive for diagnosing Pd allergy with a standardized LTT. Patients/methods: After determining optimal nontoxic and nonmitogenic concentrations for Na₂[PdCl₄], blood samples from 105 patients with clinical suspicion of metal allergy were tested with an LTT called memory lymphocyte immuno stimulation assay for Na₂[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 Na₂[PdCl₄]. All positive results to PdCl₂ were covered by Na₂[PdCl₄]. From the 30 positive reactions to Na₂[PdCl₄], 26 (87%) were concordant for NiCl₂ reactivity. Conclusion: In LTT, the use of Na₂[PdCl₄] results in more positive reactions in Pd allergy testing which are in concordance with positive reactions to PdCl₂ and NiCl₂.