What is the Tacrolimus (Prograf/FK506) Test?

The Tacrolimus blood level test measures the concentration of tacrolimus, also known as Prograf or FK506, in the bloodstream. Tacrolimus is a potent immunosuppressant used primarily to prevent organ rejection after transplantation and in certain autoimmune conditions.

Because tacrolimus has a narrow therapeutic range, even small changes in blood levels can affect treatment effectiveness or increase the risk of side effects. Regular monitoring ensures the dose maintains immune suppression without causing harm.

This test is a key component of therapeutic drug monitoring in transplant medicine and specialist care.

Why do I need a Tacrolimus test?

Tacrolimus dosing must be carefully individualised. Factors such as kidney function, liver function, drug interactions, and time since transplant can significantly influence blood levels.

You may need this test if you:

• Have received a kidney, liver, heart, or other organ transplant
• Are taking tacrolimus long term
• Have changes in kidney or liver function
• Are starting or stopping other medications
• Experience tremors, headaches, or neurological symptoms
• Have abnormal blood test results
• Require routine post-transplant monitoring

Accurate monitoring helps prevent rejection, toxicity, and long-term complications.

Benefits of the test

1. Ensures effective immunosuppression
   Confirms tacrolimus levels are sufficient to prevent rejection.
2. Reduces toxicity risk
   Identifies elevated levels that may harm kidneys or nerves.
3. Supports transplant graft survival
   Maintains optimal drug exposure over time.
4. Guides precise dose adjustment
   Allows clinicians to fine-tune therapy safely.
5. Detects drug interactions early
   Identifies level changes caused by other medications.
6. Essential for long-term transplant care
   Critical for ongoing monitoring post-transplant.
7. Objective and measurable
   Provides clear numeric results rather than symptom-based decisions.
8. Improves overall treatment safety
   Helps balance rejection prevention with side-effect control.

Step-by-step: How we offer testing

Clinic-based testing (UK-wide)

• Choose your nearest UK clinic
• Attend your appointment
• A clinician draws a blood sample (trough level, pre-dose)
• Sample is sent to the laboratory
• Results are issued once analysis is complete

Home or hotel visit (+£60, UK-wide)

• Book a mobile phlebotomist
• Blood sample taken at your home or hotel
• No need to travel to a clinic
• Sample securely transported to the laboratory

Your results explained

Low levels (sub-therapeutic)

• Tacrolimus concentration below target range
• UK standard (typical): <5 ng/mL (target varies by transplant type and time post-transplant)
• May increase risk of organ rejection

Normal levels (therapeutic range)

• Tacrolimus within target treatment window
• UK standard (typical): 5–15 ng/mL
• Indicates appropriate immunosuppressive control

High levels (risk of toxicity)

• Tacrolimus concentration above target range
• UK standard (typical): >15–20 ng/mL
• Increased risk of kidney damage, tremor, and neurological effects