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.
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.
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.
- Sample of whole blood
- We perform the test upon request