Thyroid hormone total serum concentration (T₃)
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.
["Understanding your T₃ levels can help assess thyroid function and overall health."]
Key facts at a glance
- LOINC
- 47197-9
- Short code
- T3 sp8 p chal SerPl-sCnc
- Synonyms
- T3 sp8 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 Is Triiodothyronine (T₃)?
Triiodothyronine (T₃) is a hormone produced by your thyroid gland. It plays a crucial role in controlling metabolism, brain development, and maintaining normal body temperature. While thyroxine (T₄) is the primary hormone produced by the thyroid, T₃ is more biologically active and helps regulate many of the body’s functions, including heart rate, digestion, and muscle function.
Why Might You Need This Test?
Your healthcare provider may order a T₃ test to diagnose or monitor conditions related to thyroid dysfunction, such as hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). It can also be used to evaluate symptoms like fatigue, weight changes, or unexplained heart issues.
How Is the Test Performed?
A blood sample is taken from a vein in your arm. The sample is sent to a lab where it is analyzed to measure the total concentration of T₃ in your serum. This test does not require fasting unless specified by your provider.
What Do Results Mean?
Results are interpreted in the context of your overall health and other thyroid-related tests. Abnormal levels may indicate thyroid hormone imbalances, but they are not standalone diagnoses. Your provider will discuss findings with you and may recommend additional testing or adjustments to treatment.
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 Serum Triiodothyronine (T₃)
Frequently asked questions
What Are Common Causes of Abnormal Results?
How Often Should I Get This Test?
Can I Prepare for This 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