Tacrolimus, Whole Blood

TEST: 700248
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CPT: 80197
Updated on 01/30/2025
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Synonyms

  • FK506
  • Prograf®
  • Protopic®

Expected Turnaround Time

2 - 3 days

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Related Documents

Specimen Requirements

Specimen

Whole blood

Volume

1 mL

Minimum Volume

0.6 mL (Note: This volume does not allow for repeat testing.)

Container

Lavender-top (EDTA) tube

Storage Instructions

Room temperature

Patient Preparation

Trough levels are most reproducible.

Causes for Rejection

Plasma or serum specimen

Test Details

Use

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.

Limitations

Specimens from patients who have circulating human antimouse (HAMA) as a result of having received mouse monoclonal antibodies may give falsely elevated or depressed results in this assay.

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.

Methodology

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Reference Interval

5.0–20.0 ng/mL

Clinical studies have shown that patients administered 0.07 mg/kg Prograf® obtain an optimal response to the drug at the following trough levels:

• Trough (immediately following transplant): 15.0 ng/mL

• Trough (steady-state, two weeks or more after transplant): 3.0−8.0 ng/mL

5.0–20.0 ng/mL

Additional Information

Tacrolimus, previously known as FK506, is an immunosuppressive drug derived from Streptomyces tsulenbaensis. 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 phosphatase activity of calcineurin, although the exact mechanism of action is not known. Tacrolimus is bound to plasma proteins and is highly bound to erythrocytes (ratio of whole blood:plasma ranging from 12 to 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 liver 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, ritonavir, 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

Footnotes

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

References

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

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