Falsely elevated tacrolimus concentrations measured using the ACMIA method due to circulating endogenous antibodies in a kidney transplant recipient.

Background: Therapeutic monitoring of whole-blood concentration of tacrolimus, a potent immunosuppressive drug used after organ transplantation, is essential to avoid toxic effects and to maintain the correct dosage. Although the reference method for the determination of tacrolimus concentrations is LC-MS/MS, several certified immunoassays are widely used for routine examinations. We report falsely elevated blood tacrolimus concentrations using the antibody-conjugated magnetic immunoassay (ACMIA) from Siemens Healthcare Diagnostics for the analysis of a patient who had undergone renal transplantation.