Tacrolimus Test (Tacrolimus FK506 Test)

Tacrolimus Test

It is a test done to measure the level of tacrolimus drug in blood, in patients who are taking this drug. Tacrolimus is also called FK506. Tacrolimus is an immunosuppressant drug, given to organ transplant recipients, to minimize the immune response in the recipient’s body.

Organ transplantation is a procedure where organs from one person (donor) is removed and placed in the body of another person (recipient) to replace the deficient or inefficient vital organ. The organs most commonly transplanted are liver, lungs, kidney, heart etc.

The major problem that can occur with organ transplantation is rejection. This rejection can cause severe consequences in the recipient. This happens due to activation of the immune system in the recipient. Since the function of immune system is to destroy any outside invaders like bacteria, virus and parasites, it may be activated against the donor organ considering it to be foreign body. The types of rejections are categorised as:

• Hyper acute rejection-this rejection happens within minutes of completion of surgery. This type of rejection may even cause death.
• Acute rejection-it may happen from first week after surgery to three months after. It is a common type of rejection met in almost all recipients.
• Chronic rejection-it happens over a long span of time of many years. This causes damage to the transplanted organ over prolonged period.

This rejection can be minimised by the use of certain drugs called immunosuppressive drugs. Tacrolimus is a type of immunosuppressive drug that suppresses the activation of T- lymphocytes (which form a part of immune system) and hence prevents organ rejection. This drug is given orally or intravenously to the recipient.

In tacrolimus test the blood levels of tacrolimus drug is measured to maintain it in therapeutic range. This is because if the blood level of tacrolimus is low it may cause organ rejection. And if blood levels is high it may cause toxicity especially kidney damage.

Why is the Tacrolimus blood test prescribed?

The healthcare provider may advise this test to assess the tacrolimus levels in blood. This is important to keep its level in therapeutic range. The side effects of high tacrolimus levels are:

• Kidney toxicity
• Headache
• High blood pressure
• Seizures
• Tremors
• Nausea/vomiting

Procedure and Prerequisites

The sample for tacrolimus blood test is taken from blood by inserting a small needle into vein arm. A small amount of blood is then collected in a test tube or vial. There may be a little pain due to needle prick. The ideal sampling time is just before the next dose. The date and time of sample collection should be mentioned as well as dose of the drug.

Reference Range

• Therapeutic reference range-5to15 ug/l
• The range may vary from lab to lab