Tacrolimus, Immunoassay

CPT: 80197
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Test Details


  • FK506
  • Prograf®
  • Protopic®


Tacrolimus is an immunosuppressive drug that is believed to prevent rejection in transplantation patients. Measurement of tacrolimus blood levels may be of use in monitoring patients receiving this drug.


Patient samples may contain heterophilic antibodies that could react in immunoassays to give falsely elevated or depressed results. Antibodies to β-galactosidase can be encountered in samples as a consequence of bacterial infection and may produce falsely elevated results that may not be consistent with clinical evaluation.


Microgenics QMS immunoassay

Additional Information

Tacrolimus is an immunosuppressive drug that is believed to prevent rejection in transplantation patients. Measurement of tacrolimus blood levels may be of use in monitoring patients receiving this drug. Tacrolimus, previously known as FK506, is an immunosuppressive drug derived from the bacterium Streptomyces tsukubaensis. It has been shown to be effective for the treatment of rejection following liver and kidney transplantations. Clinical trials are continuing for a variety of indications. Tacrolimus inhibits T-lymphocyte activation by inhibition of the phosphate activity of calcineurin, although the exact mechanism of action is not known. Tacrolimus is bound to plasma proteins and is highly bound to erythrocytes (ration of whole blood:plasma ranging from 12−67). Tacrolimus may be administered IV or orally. Absorption from the GI tract is variable and irregular. Peak blood concentrations are achieved at 1.5 to 3.5 hours. The elimination half-life from whole blood is 11.7 hours in transplant patients. Tacrolimus can cause nephrotoxicity, particularly when used in high doses. Care must be taken if tacrolimus is used in combination with other immunosuppressive drugs, particularly cyclosporine. Drugs found to increase tacrolimus levels include diltiazem, verapamil, clotrimazole, fluconazole, ketoconazole, voriconazole, clarithromycin, erythromycin, nelfinavir, torinavir, as well as grapefruit juice. Decreased tacrolimus levels have been found with coadministration of rifampicin, phenytoin, carbamazepine, phenobarbital, octreotide, and St John's wort.1

Specimen Requirements


Whole blood


1 mL

Minimum Volume

0.3 mL


Lavender-top (EDTA) tube


Specimens collected in EDTA tubes may be stored for seven days at 2°C to 8°C prior to being tested.

Storage Instructions

Room temperature

Stability Requirements



Room temperature

7 days


7 days


2 months

Causes for Rejection

Plasma or serum specimen

Clinical Information

Special Instructions

If the preferred methodology for tacrolimus is liquid chromatography/tandem mass spectrometry (LC/MS-MS), please order test 700248.


1. Bernardo JF, McCauley J. Drug therapy in transplant recipients: Special considerations in the elderly with comorbid conditions. Drugs Aging. 2004; 21(5):323-348. 15040759


Alak AM. Measurement of tacrolimus (FK506) and Its metabolites: A review of assay development and application in therapeutic drug monitoring and pharmacokinetic studies. Ther Drug Monit. 1997; 19(3):338-351. 9200777
Siemens Dimension. Tacrolimus [package insert]. March 10, 2009.


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
711034 Tacrolimus by Immunoassay 74096-9 711037 Tacrolimus by Immunoassay ng/mL 74096-9

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