Puzzling interference in the Siemens tacrolimus assay in a renal transplant patient: A case report

Therapeutic drug monitoring is a key tool for optimizing tacrolimus therapy in transplant recipients. The modified ACMIA assay from Siemens Healthcare Diagnostics is an immunoassay commonly used for tacrolimus monitoring, but it is not known whether this assay is resistant to interference from endogenous substances in real-world use.

To describe a case of unexpected interference in tacrolimus monitoring using the modified ACMIA method in a kidney transplant recipient, and to highlight the importance of careful interpretation of laboratory results and effective communication with clinicians in optimizing patient care.

This case report describes a significant interference in the monitoring of tacrolimus in a kidney transplant recipient using the new ACMIA method. In this case, when aberrant results for tacrolimus were found using the new ACMIA method, they were re-analyzed using the CMIA method from Abbott. The presence of positive ANCA-MPO autoantibodies was found to be the most likely cause of the interference after an extensive workup.

This is the first report of major interference with the modified ACMIA tacrolimus method and emphasizes the importance of proper interpretation of laboratory results and effective communication with clinicians in optimizing patient care.