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Tacrolimus trough concentration (serum/plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of tacrolimus, a medication used to prevent organ rejection after a transplant, in your blood at its lowest point before the next dose.

Quick summary

["Tacrolimus levels help doctors adjust your medication to avoid side effects while keeping your immune system suppressed safely."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
33929-1
Short code
Tacrolimus Trough SerPl-mCnc
Synonyms
Tacrolimus Trough SerPl-mCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Doctors order this test to monitor your tacrolimus blood levels, especially after a transplant. It helps ensure your dose is correct to prevent rejection of the transplanted organ or excessive immunosuppression, which can increase infection risk.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into a vein in your arm or hand for blood collection. The process is quick and usually painless.

What the Test Results Mean

Results help your healthcare team determine if your tacrolimus dose is appropriate. Too high or too low levels can affect your health, so follow-up tests may be scheduled to adjust your medication.

Common Side Effects to Watch For

Tacrolimus can cause side effects like nausea, headache, or increased risk of infections. If you experience unusual fatigue, skin rashes, or signs of infection (like fever or sore throat), contact your doctor.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Monitoring Tacrolimus Levels Ensures Optimal Transplant Care

Short name

Tacrolimus Level (Trough)

Frequently asked questions

How often will I need this test?
Your doctor will schedule follow-up tests based on your transplant timeline and how your body responds to the medication. Typically, tests are done weekly or monthly during the early stages and less frequently afterward.
Can I eat or drink before this test?
You can eat and drink normally before the test, as it’s a blood draw and doesn’t require fasting.
What if my tacrolimus level is too high or too low?
If levels are too high, your doctor may reduce your dose to lower the risk of side effects. If levels are too low, they may increase your dose to prevent organ rejection. Your doctor will guide you on adjustments.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy