title: Specificity of a circulating antibody that interferes with a widely used tacrolimus immunoassay.
abstract: Accurate measurement of whole-blood tacrolimus concentration is essential for achieving therapeutic immunosuppression and minimizing toxicity in renal transplant recipients. Falsely elevated or decreased values may trigger unnecessary dose adjustments. We identified a falsely elevated whole-blood tacrolimus immunoassay result in a renal transplant patient. Twelve hours after the patient received his first dose, the blood concentration was 24.4 ng/mL using the Siemens Dimension RxL immunoassay. Immunoabsorption studies showed that the cause of the interference was an endogenous antibody present in the patient's plasma that recognized a unique epitope present on the antibody-enzyme (beta-galactosidase) conjugate used in the Siemens tacrolimus immunoassay but not on the antibody or beta-galactosidase alone. This report adds to the growing knowledge base of endogenous antibody interferences in diagnostic immunoassays. To our knowledge, this is the first such report of a falsely elevated tacrolimus concentration due to recognition of an epitope present only on the monoclonal antibody-enzyme conjugate.
authors.affiliation: Department of Pathology and Immunology, Washington University, St. Louis, MO 63110, USA.
authors.forename: Bijal A
authors.initials: BA
authors.lastname: Parikh
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Siedlecki
authors.forename: Mitchell G
authors.initials: MG
authors.lastname: Scott
mesh_terms: D000328:Adult; D000906:Antibodies / Q000097:blood*; D001667:Binding, Competitive; D006801:Humans; D007118:Immunoassay / Q000592:standards; D007676:Kidney Failure, Chronic / Q000097:blood / Q000188:drug therapy; D016030:Kidney Transplantation / Q000276:immunology; D008297:Male; D016559:Tacrolimus / Q000097:blood* / Q000627:therapeutic use; D013678:Technology, Pharmaceutical / Q000379:methods / Q000592:standards*
chemical_list: D000906:Antibodies; D016559:Tacrolimus