Validity of MELISA for metal sensitivity testing.

OBJECTIVE: This study was carried out to evaluate the reproducibility, sensitivity, specificity, and reliability of the MELISA Test for detecting metal sensitivity in patients with clinical symptoms of a type IV hypersensitivity to metal.

DESIGN: Blood from 250 patients was tested in MELISA against up to 20 different metals in 2 to 3 concentrations. The frequency and distribution of metal reactivities, the sensitivity and specificity of nickel reactivity in patients with and without confirmed or suspected sensitivity to nickel, and the roles of lymphocyte concentration and concentration of inorganic mercury were analyzed. In addition, for reproducibility testing, 196 metal tests were performed in duplicate, and intra- and interassay variations of MELISA results were examined in patients patch-test positive for the relevant metal.

RESULTS: Among the 250 patients, reactivity to 0, 1, 2, 3, 4, or > or = 5 metals was 26%, 36%, 15%, 12%, 6%, and 5%, respectively. Reactivity was most frequent to nickel (73%), followed by titanium (42%), cadmium (18%) gold (17%), palladium (13%), lead (11%), beryllium (9%), inorganic mercury (8%), tin (8%), and phenylmercury (6%). All patients (n=15) with confirmed or suspected nickel allergy were positive in MELISA, while patients with no suspicion of nickel allergy were either negative (n=6) or very low positive (n=4) in MELISA. MELISA reactivity is directly dependent on lymphocyte concentration: the higher the lymphocyte concentration per test, the stronger the reactivity. Concentrations of inorganic mercury > 0.5 microg/ml cause non antigen-specific (mitogenic) reactions in a majority of patients. The reproducibility rate was 94% using a cut-off of Stimulation Index > or = 3 or 99% using a cut-off of > or = 5. While the absolute intra- and interassay Stimulation Index values may vary, the qualitative results are highly reproducible.

CONCLUSION: The MELISA Test is reproducible, sensitive, specific, and reliable for detecting metal sensitivity in metal-sensitive patients.