Free triiodothyronine (T₃) with triple bolus administration (serum/plasma concentration)
This test measures the amount of free thyroid hormone T₃ in your blood, which plays a key role in regulating metabolism and energy levels. Free T₃ is the active form of thyroid hormone that circulates independently of thyroid-binding proteins.
Assessing your free T₃ level helps doctors evaluate thyroid function and identify potential thyroid disorders.
Key facts at a glance
- LOINC
- 40327-9
- Short code
- T3Free pre Triple Bolus SerPl-sCnc
- Synonyms
- T3Free pre Triple Bolus 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 Might Be Ordered
Your healthcare provider may recommend this test if you have symptoms like fatigue, weight changes, or unexplained issues with metabolism. It could also be used to monitor thyroid conditions such as hypothyroidism or hyperthyroidism, especially when combined with other thyroid tests like TSH (thyroid-stimulating hormone).
What to Expect Before the Test
No special preparation is typically required for this test. You may have a blood draw from a vein in your arm. If you are taking thyroid medications, let your doctor know beforehand to avoid potential interference with results.
What the Results Mean
Free T₃ levels can vary based on individual health, diet, and other medical conditions. While reference ranges can differ by lab, abnormal results may suggest thyroid dysfunction. Your doctor will interpret the results in the context of your overall health and other tests.
Common Conditions Linked to Free T₃ Levels
High free T₃ levels may indicate hyperthyroidism (overactive thyroid), while low levels can suggest hypothyroidism (underactive thyroid) or other thyroid-related issues. It can also be used to assess thyroid function in patients with thyroid nodules or after thyroid surgery.
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.
Free T₃ is an important marker for thyroid hormone activity because it reflects the biologically active portion of thyroid hormone in your blood. It can provide additional insight beyond TSH alone, especially in cases where TSH levels are normal but thyroid symptoms persist. This test is often used in conjunction with other thyroid tests to get a comprehensive picture of thyroid health.
Short name
Free T₃ (Triiodothyronine) Level
Frequently asked questions
Will I need to prepare for this test in any way?
What does a low or high free T₃ level mean?
Can free T₃ levels change over time?
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