Thyroid hormone total triiodothyronine (T3) mass concentration in serum
This test measures the total amount of the hormone triiodothyronine (T3) in your blood. T3 is a key hormone produced by your thyroid gland that helps regulate metabolism.
["Your doctor may order this test to check thyroid function or monitor treatment for thyroid disorders."]
Key facts at a glance
- LOINC
- 83124-8
- Short code
- T3 SerPl IA-mCnc
- Synonyms
- T3 SerPl IA-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
- Method
- ia
- 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 request a total T3 test if you have symptoms of thyroid problems, such as unusual fatigue, weight changes, or heart palpitations. It can also be used to evaluate thyroid function during treatment for conditions like hypothyroidism or hyperthyroidism, or to monitor thyroid hormone replacement therapy.
What Does the Test Measure?
Total T3 measures the combined levels of active T3 hormone in your blood. While T3 is directly active in your body, it is primarily produced from thyroxine (T4) through a process involving the enzyme deiodinase. This test helps assess overall thyroid hormone availability in your system.
How Is the Test Performed?
A blood sample is drawn from a vein, usually in your arm. The sample is then sent to a lab for analysis using a specialized method to measure the total T3 concentration in your serum.
What Are Common Causes for Testing?
Tests for total T3 may be ordered when there are suspected thyroid issues, such as underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid conditions. It can also be used to diagnose or monitor conditions like Hashimoto’s disease, Graves’ disease, or thyroid nodules.
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.
Clinical Significance
Short name
Total T3
Frequently asked questions
What Are Normal Results?
How Do I Prepare for This Test?
What Are Possible Abnormal Results?
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