Also Known As
FK506
TAC
Formal Name
Tacrolimus
This article was last reviewed on
This article waslast modified on
May 27, 2018.
At a Glance
Why Get Tested?

To determine the level of the drug tacrolimus in your blood in order to establish a dosing regimen, maintain therapeutic levels, and detect toxic levels

When To Get Tested?

As soon as tacrolimus therapy begins, frequently at first, then at regular intervals to monitor concentrations over time

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

The sample should be collected 12 hours after your last dose and immediately prior to your next dose or as directed by your health practitioner.

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Tacrolimus is an immunosuppressive drug that is given orally or intravenously to people who have had a kidney, liver, heart, or other organ transplant. It is a potent drug that helps to prevent rejection of the transplanted organ by the body. This test measures the amount of tacrolimus in the blood.

Normally, a person's immune system recognizes a new, transplanted organ as foreign and begin to attack it. Tacrolimus limits this response and helps to prevent organ rejection by inhibiting the activation of certain immune cells called T-lymphocytes.

The level of tacrolimus in the blood must be maintained within a narrow therapeutic range. If the concentration is too low, organ rejection may occur; if it is too high, then the person may experience symptoms associated with toxicity.

Dosages must be tailored to the individual. Often, people will begin with higher doses of tacrolimus at the start of therapy and then decrease the dose over the next few weeks.

Tacrolimus is usually taken twice a day at set intervals before or after meals. When a person takes a dose, the blood concentration rises and peaks within about 2 to 3 hours and then begins to slowly drop. The blood test is usually measured as a "trough level," meaning that sample collection is timed for 12 hours post-dose and/or immediately prior to the next dose, when the drug's level in the blood is at its lowest.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

Is any test preparation needed to ensure the quality of the sample?

The sample should be collected 12 hours after the last dose and immediately prior to the next dose or as directed.

Accordion Title
Common Questions
  • How is it used?

    The tacrolimus test is used to measure the amount of the 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 between the dose of tacrolimus given and the level of drug in the blood. 
    • How individuals absorb and metabolize oral doses of tacrolimus can vary greatly depending on the time of the dose and what, if any, food the person has eaten. 
    • Tacrolimus can cause kidney damage (nephrotoxicity), especially in high doses. Measuring levels in people 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 can increase the risk of developing serious bacterial, viral, fungal, and protozoal infections because it decreases the body's immune response.
  • When is it ordered?

    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, the frequency of tacrolimus testing may be decreased. The test is also performed when dosages are changed and whenever someone has symptoms that suggest side effects, toxicity, or organ rejection.

    Signs and symptoms of tacrolimus toxicity vary according to the type of organ transplant and may include:

    • Kidney damage (nephrotoxicity)
    • Tremors, headache (neurotoxicity)
    • High blood pressure
    • Nausea and vomiting
    • Electrolyte disturbances, such as hyperkalemia
    • Intermittent and/or persistent ringing or roaring in the ears (tinnitus)
    • Seizures
    • Elevated heartbeat
    • Blurred vision

    Monitoring at intervals is necessary as long as someone is taking tacrolimus.

  • What does the test result mean?

    A concentration that is higher than the established therapeutic range may increase the risk of associated toxicity, including damage to the kidneys and nerves. A concentration that is too low may lead to rejection of the transplanted organ. Side effects may be seen at any dosage but tend to be more severe with a higher tacrolimus level.

    The therapeutic range established by a laboratory will depend on both the method used to measure the drug and the type of transplant. Results from different methods are not interchangeable. A health practitioner will usually send samples sent consistently to the same laboratory and will be guided by that laboratory's therapeutic ranges.

  • Is there anything else I should know?

    A variety of drugs can increase or decrease tacrolimus levels in the blood. These include calcium channel blockers, antifungal drugs, macrolide antibiotics (such as erythromycin), protease inhibitors, chloramphenicol, and other immunosuppressants, anticonvulsants, and antimicrobials. Tell your health practitioner about any other medications you take, especially cyclosporine, sirolimus, nelfinavir telaprevir, boceprevir, and amiodarone. Many other prescription drugs, grapefruit juice, and herbal supplements such as St. John's Wort can also interact with tacrolimus.

    Topical tacrolimus may be used to treat a variety of skin conditions, such as eczema, that have not responded well to other medications. This topical use of tacrolimus is intended to be local, not systemic, and is not usually monitored.

    Tacrolimus increases the risk of developing malignancies such as lymphoma and skin cancer, so sunlight should be avoided when taking this drug. It can also cause new onset diabetes, especially in African Americans and Hispanics so a health practitioner may monitor a person's glucose levels. Tacrolimus may also cause QT prolongation, a condition that affects heart rhythm.

    People should not alter their dose or the time that they take their dose without consulting with their health care provider. Tacrolimus should be taken consistently with respect to meals. Food, especially high-fat meals, can significantly reduce the bioavailability (amount of the drug that reaches the circulation) compared with fasting.

    Women who are pregnant or planning to become pregnant should talk to their health practitioner about associated risks.

  • How long will I need to be on tacrolimus?

    Transplant recpients must take tacrolimus or a different immunosuppressant (or combination of drugs) throughout their life. Talk to your health practitioner about the best choice for your condition. This choice may change over time.

  • Who orders tacrolimus tests?

    Tacrolimus will usually be monitored by the transplant team that performed the transplant or by a health practitioner who has specific knowledge of the condition or disease for which the drug is prescribed.

  • Should I tell my other health care providers that I am taking tacrolimus?

    Yes, this is important information for them to have, partially because of drug interactions and partially because of the immunosuppressive action of tacrolimus. It can affect your ability to heal, to get vaccinations, and may increase your risk of developing certain cancers (such as skin cancers).

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