title: Falsely elevated tacrolimus levels caused by immunoassay interference secondary to beta-galactosidase antibodies in an infected liver transplant recipient.
abstract: Careful interpretation of tacrolimus levels is essential to ensure optimal immunosuppressive therapy while avoiding toxicity. Interference with tacrolimus assays may be an underreported event that has the potential to result in negative patient outcomes through unnecessary modifications of therapy. We describe a 55-year-old liver transplant recipient who had falsely elevated tacrolimus levels that led to the eventual disruption of his immunosuppressive therapy and subsequent rejection of his allograft.Although his increased tacrolimus levels did not correlate with clinical signs and symptoms of tacrolimus toxicity, interruption of therapy in this patient was supported by an acute infection and a slight elevation in serum creatinine concentration. Tacrolimus levels were analyzed by using an antibody conjugated magnetic immunoassay method, and levels as high as 79.7 ng/ml were observed, despite discontinuation of tacrolimus. We conducted an evaluation for assay interference by using an alternative assay method(microparticle enzyme immunoassay), by testing plasma samples that were not hemolyzed, and by analyzing levels of an unrelated drug that uses the same technology as the initial tacrolimus assay. beta-galactosidase antibodies were ultimately confirmed as the cause of the immunoassay interference. Inpatients receiving tacrolimus, spuriously high tacrolimus levels should be carefully evaluated, and drastic adjustments to therapy should be made only within the context of clinical toxicity.
authors.forename: John P
authors.initials: JP
authors.lastname: Knorr
authors.forename: Kevin S
authors.initials: KS
authors.lastname: Grewal
authors.forename: Manjula
authors.initials: M
authors.lastname: Balasubramanian
authors.forename: Nancy
authors.initials: N
authors.lastname: Young
authors.forename: Radi
authors.initials: R
authors.lastname: Zaki
authors.forename: Kamrin
authors.initials: K
authors.lastname: Khanmoradi
authors.forename: Victor
authors.initials: V
authors.lastname: Araya
authors.forename: Jorge
authors.initials: J
authors.lastname: Ortiz
mesh_terms: D000906:Antibodies / Q000097:blood*; D005189:False Positive Reactions; D006084:Graft Rejection; D006801:Humans; D007118:Immunoassay; D007124:Immunoenzyme Techniques; D007166:Immunosuppressive Agents / Q000097:blood* / Q000627:therapeutic use; D016031:Liver Transplantation; D008297:Male; D008875:Middle Aged; D016559:Tacrolimus / Q000097:blood* / Q000627:therapeutic use; D001616:beta-Galactosidase / Q000276:immunology*
chemical_list: D000906:Antibodies; D007166:Immunosuppressive Agents; D001616:beta-Galactosidase; D016559:Tacrolimus