Thyroid hormone total triiodothyronine (T3) concentration in serum/plasma
This test measures the total amount of the hormone triiodothyronine (T3) in your blood, which plays a key role in regulating metabolism and energy levels.
["Total T3 helps assess thyroid function and identify potential thyroid disorders."]
Key facts at a glance
- LOINC
- 35231-0
- Short code
- T3 SerPl-msCnc
- Synonyms
- T3 SerPl-msCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 80
- Ref high
- 200
- Critical range
- 20 N/A – 400 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84436
- SNOMED
- 302346007
- 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?
Your healthcare provider may order this test if you have symptoms like fatigue, weight changes, or unexplained heart issues, or if they suspect thyroid problems. It can also be part of routine thyroid function testing or monitoring for conditions like hypothyroidism or hyperthyroidism.
What to Expect Before the Test
No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if blood is drawn early in the morning. Wear comfortable clothing for easy access to your arm.
How the Test Is Performed
A healthcare professional will insert a needle into a vein in your arm to draw a blood sample. You may feel a slight pinch, but the procedure usually takes just a few minutes.
What the Results Mean
Results alone don’t diagnose a condition—they’re used alongside other tests and symptoms. Abnormal levels may signal thyroid dysfunction, but further evaluation (like TSH testing) is often needed.
Reference range
Adult: 80-200 ng/dLN/A
Take your thyroid medication after the blood draw if applicable. No fasting required.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated T3 levels may indicate hyperthyroidism (overactive thyroid), while low levels can suggest hypothyroidism (underactive thyroid) or other thyroid or pituitary issues. It’s often measured alongside TSH to confirm or refine diagnosis.
Short name
Total T3
Frequently asked questions
What causes abnormal T3 levels?
How long does it take to get results?
Can diet or supplements affect T3 test results?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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 17, 2026. · Read our editorial policy