Lack of Specificity of Cyclosporine Immunoassays

Abstract

Abstract Objective.—To evaluate the cross-reactivity of the 6 most abundant cyclosporine A (CsA) metabolites in commonly used assays for CsA. Design.—Whole blood samples containing either only 62 ng/mL CsA (A) or 62 ng/mL CsA and between 49 and 86 ng/mL of 1 of the 6 most abundant CsA metabolites (B) were lyophilized. One sample of A and 1 of B were mailed to each of the laboratories participating in the College of American Pathologists Proficiency Testing Program quarterly during a 3-year period (1999–2001). Method means and coefficients of variation were calculated for each mailing. Results.—The study showed significant cross-reactivity of metabolites in all the immunoassay systems studied. Overall degree of interference decreased from Abbott TDx polyclonal > Abbott TDx monoclonal > DiaSorin > Syva EMIT. High-performance liquid chromatography methods gave results close to those found using mass spectrometric techniques. Conclusions.—Significant metabolite interference was found to occur with the immunoassay systems studied.