Sodium tetrachloropalladate for diagnosing palladium sensitization

Background. Exposure to palladium (Pd) may lead to clinical allergic reactions. With frequent nickel (Ni) exposure and cross-reactivity between Ni and Pd at the T cell recognition level, positive Pd reactions on patch testing are surprisingly uncommon. PdCl2 is often used for epicutaneous patch testing. Objectives. To compare the sensitivity and specificity of sodium tetrachloropalladate (Na2PdCl4) and PdCl2 for Pd patch testing in metal-allergic patients and non-allergic controls. Methods. Twenty-six metal-allergic patients and 26 non-allergic controls were selected on the basis of detailed medical histories. Patch test results were used to determine the diagnostic performance of the two Pd salts as compared with NiSO4. Results. With three outliers in both groups, the sensitivity/specificity were calculated to be 42%/96% for PdCl2, 65%/92% for Na2PdCl4, and 77%/92% for NiSO4. Furthermore, of all (n = 19) Na2PdCl4 reactors, 17 (89%) also showed positive reactions to NiSO4. Conversely, of all (n = 22) NiSO4 reactors, 17 (77%) showed concomitant positive reactions to Na2PdCl4. Conclusions. Positive test reactions to Na2PdCl4 are confirmed by large-scale concordant reactions to PdCl2 and NiSO4. Although statistical significance was not reached, the increased sensitivity has important clinical relevance, as false-positive results are rare. Incorporation of Na2PdCl4 into standard and/or dental screening patch test series is suggested