Sodium tetrachloropalladate (Na2[PdCl4]) as an improved test salt for palladium allergy patch testing

Background: In the last decades, palladium is widely used in dentistry. Allergic reactions to palladium are rarely diagnosed with patch testing, even when positive results would be expected. Palladium tends to cross-react with nickel, which should give rise to more positive reactions to palladium dichloride (standard test salt).
Objective: The aim of the study was to test whether or not mono-nuclear sodium tetrachloropalladate (Na-2[PdCl4]) in petrolatum is a better test salt for diagnosing palladium allergy. Positive reactions to the investigated test salt are compared not only with PdCl2(aq.), but also to NiSO4(aq.) and NiSO4(pet.).
Patients/Methods: Concentration series of Na-2[PdCl4] were carried out. 164 consecutive patients were patch tested.
Results: 3% of Na-2[PdCl4]((pet.)) was found to be the highest non-irritative concentration. The results show (n = 164) that Na-2[PdCl4] covers all reactions to PdCl2 (1.8%) and provokes more positive reactions (14%). From the 164 patients, 18.3% reacted positively to at least 1 of the nickel salts.
Conclusion: The sensitivity of patch testing with Na-2[PdCl4] is increased compared with the PdCl2 salt. Therefore, it can be concluded that Na-2[PdCl4] is to be a better test salt for diagnosing palladium allergy with patch testing.