Specificity of a circulating antibody that interferes with a widely used tacrolimus immunoassay

Bijal A. Parikh, Andrew M. Siedlecki, Mitchell G. Scott

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14 Scopus citations


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 (β-galactosidase) conjugate used in the Siemens tacrolimus immunoassay but not on the antibody or β-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.

Original languageEnglish
Pages (from-to)228-231
Number of pages4
JournalTherapeutic Drug Monitoring
Issue number2
StatePublished - Apr 2010


  • Immunoassay
  • Interference
  • Tacrolimus


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