Thyroid hormone total triiodothyronine (T₃) concentration
This test measures the total amount of the hormone triiodothyronine (T₃) in your blood. T₃ is one of the primary active thyroid hormones that helps regulate metabolism.
["Your doctor may order this test to assess thyroid function or evaluate symptoms related to thyroid issues."]
Key facts at a glance
- LOINC
- 47194-6
- Short code
- T3 sp5 p chal SerPl-sCnc
- Synonyms
- T3 sp5 p chal SerPl-sCnc
- 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 This Test Is Done
Doctors may request a total T₃ test to diagnose or monitor conditions such as hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), or thyroid hormone imbalances. It can also be used to evaluate the effectiveness of thyroid hormone replacement therapy or to check for thyroid dysfunction in certain genetic or autoimmune disorders.
What to Expect Before the Test
No special preparation is usually needed for this blood test. You may be asked to fast for 8–12 hours before the draw if your doctor specifies it, but this is less common for T₃ testing alone. Bring any medications you’re taking to your appointment.
What Happens During the Test
A healthcare provider will draw blood from a vein in your arm. The process is quick and typically painless, though you may feel a slight pinch. The blood sample is then sent to a lab for analysis using an immunoassay method to measure T₃ levels.
What the Results Mean
Results alone don’t provide a full picture of thyroid health. They’re usually interpreted alongside other thyroid tests (like TSH or free T₃) and clinical symptoms. Abnormal levels may signal thyroid dysfunction, but further evaluation is needed to determine the cause.
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.
◆Associated findings1
Short name
Total T₃
Frequently asked questions
How long does it take to get my T₃ test results?
Can I eat or drink before this test?
What are the most common reasons doctors order a T₃ test?
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