Thyroid hormone total triiodothyronine (T₃) in serum/plasma
This test measures the total amount of the hormone triiodothyronine (T₃) in your blood. T₃ is one of the key hormones produced by your thyroid gland that helps regulate metabolism.
["Your doctor may check T₃ levels to assess thyroid function and overall metabolism."]
Key facts at a glance
- LOINC
- 12957-7
- Short code
- T3 sp6 p chal SerPl-mCnc
- Synonyms
- T3 sp6 p chal SerPl-mCnc
- 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 a total T₃ test to evaluate thyroid health, especially if you have symptoms like fatigue, weight changes, or mood swings. It can also be used alongside other thyroid tests to help diagnose conditions such as hypothyroidism or hyperthyroidism, or to monitor treatment for thyroid disorders.
What Does a Result Mean?
Results can vary based on individual health, age, and other factors. While reference ranges exist, they can differ slightly between labs. Your doctor will interpret your results in the context of your overall health and symptoms.
Sample Collection and Preparation
A blood sample is typically drawn from a vein in your arm. You may be asked to fast for a few hours before the test, but this is not always required. The blood is sent to a lab for analysis.
Common Conditions Monitored or Diagnosed
Total T₃ levels can help diagnose or monitor conditions like thyroid dysfunction, including hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It may also be used to check for other metabolic or endocrine issues.
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.
Total T₃ is a critical marker for thyroid hormone status. While T₃ is less abundant than thyroxine (T₄), it plays a vital role in cellular metabolism. Abnormal levels can indicate thyroid hormone imbalances, which may require medical attention to manage symptoms or underlying conditions effectively.
Short name
Total T₃
Frequently asked questions
What causes abnormal T₃ levels?
How often should I get this test?
Can diet or lifestyle affect T₃ levels?
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