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Also known as: FK506; TAC
Formal name: Tacrolimus

At a Glance

Why Get Tested?

To determine the concentration of tacrolimus in the 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

The Test Sample

What is being tested?

This test measures the amount of tacrolimus in the blood. Tacrolimus is an immunosuppressive drug that is given orally or intravenously to patients who have had a kidney, liver, heart, or other organ transplant. Normally, a person's immune system would recognise the new organ as foreign and begin to attack it. Tacrolimus limits this response and helps to prevent organ rejection by inhibiting the activation of T-lymphocytes.

Tacrolimus levels 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 patient may have symptoms associated with toxicity. Dosages must be tailored to the individual. Often, patients 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, blood concentrations rise and peak within about 2 to 3 hours and then begin to slowly drop. The blood test is usually measured as a 'trough' level. It is timed so that the collection is 12 hours post dose and/or prior to the next dose - at the drug's lowest concentration in the blood.

How is the sample collected for testing?

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

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

The Test

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.