Thyroid Hormone, Total Serum (T₃, Triiodothyronine)
This test measures the total amount of the hormone triiodothyronine (T₃) in your blood. T₃ is a key thyroid hormone that helps regulate metabolism, energy levels, and other bodily functions.
["Your T₃ levels can help doctors assess thyroid function and identify potential thyroid disorders."]
Key facts at a glance
- LOINC
- 47193-8
- Short code
- T3 sp4 p chal SerPl-sCnc
- Synonyms
- T3 sp4 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
What Does This Test Measure?
Triiodothyronine (T₃) is a hormone produced by your thyroid gland. It plays a critical role in controlling metabolism, brain development, and maintaining normal heart function. This test measures the total amount of T₃ in your serum, which includes both active and inactive forms bound to proteins in the blood.
Why Might You Need This Test?
Doctors may order this test if you have symptoms like fatigue, weight changes, heat intolerance, or cold sensitivity, or if you have a known thyroid condition. It can also be used to monitor thyroid hormone levels during treatment for thyroid disorders.
How Is the Test Performed?
A blood sample is taken from a vein, usually in your arm. The blood is then sent to a lab for analysis using a specialized immunoassay method to measure T₃ levels accurately.
What Are Common Causes of Abnormal Results?
Low T₃ levels can occur with hypothyroidism (underactive thyroid), stress, or certain medications. High T₃ levels may be seen with hyperthyroidism (overactive thyroid), certain medications, or stress-related conditions.
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 back?
Can I eat or drink anything before this test?
What are some normal variations in 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