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Tacrolimus Blood Test

The Tacrolimus Blood Test is ordered to measure tacrolimus blood levels for use in patients receiving this drug.

Test Code: 700248

Also Known As: FK506, Prograf

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

Preparation: No special preparation required.

Test Results: 3-5 days. May take longer based on weather, holiday or lab delays.



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.

The tacrolimus test is used to measure the amount of drug in the blood to determine whether the concentration has reached a therapeutic level and is below the toxic level. It is important to monitor levels of tacrolimus for several reasons:

  • There is not a good correlation, as with some other medications, between the dose of tacrolimus given and level of drug in the blood. 
  • Absorption and metabolism of oral doses of tacrolimus can vary greatly between people and even in the same person depending on the time of the dose and what, if any, food has been eaten. 
  • Tacrolimus can cause kidney damage (nephrotoxicity), especially in high doses. Measuring levels in patients who have had a kidney transplant may help to distinguish between kidney damage due to rejection (because drug level is low) and kidney damage due to tacrolimus toxicity (drug level is high).

Tacrolimus monitoring helps ensure that each individual is receiving the right amount of drug needed to treat his or her particular case.

A tacrolimus test is ordered frequently at the start of therapy, often daily when trying to establish a dosing regimen. Once dosages have been established and shown to be well tolerated, then the frequency of tacrolimus testing may be decreased. The test is performed when dosages are changed and whenever patients have symptoms that suggest side effects, toxicity, or organ rejection.

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