Thyroid hormone total serum concentration (T₃)
This test measures the total amount of active thyroid hormone triiodothyronine (T₃) in your blood, which plays a key role in regulating metabolism, growth, and energy levels.
["Your doctor may order this test to assess thyroid function or evaluate symptoms like fatigue, weight changes, or mood swings."]
Key facts at a glance
- LOINC
- 110646-7
- Short code
- T3 Msmt SerPl
- Synonyms
- T3 Msmt SerPl
- 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 T₃ test if you have symptoms such as unexplained fatigue, weight changes, anxiety, depression, or irregular heart rhythms. It can also be used to monitor thyroid hormone levels in people with thyroid disorders, such as hypothyroidism or hyperthyroidism, or during treatment for thyroid conditions.
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, but this depends on your doctor’s instructions. Wear a comfortable shirt for easy access to your arm.
What Happens During the Test
A healthcare provider will insert a small needle into a vein in your arm to draw blood. You may feel a brief pinch, but it’s usually over quickly. The blood sample is sent to a lab for analysis.
What the Results Mean
Results alone don’t provide a diagnosis—they’re often interpreted alongside other thyroid tests (like T₄ or TSH) and your medical history. Abnormal levels may indicate thyroid dysfunction, but further evaluation is 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.
◆Associated findings1
Short name
Total Serum Triiodothyronine (T₃)
Frequently asked questions
What are common symptoms or conditions this test might help diagnose?
How often should I get this test?
Can diet or medications 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