Thyroid hormone total serum concentration (T4)
This test measures the amount of total thyroid hormone (T4) in your blood. T4 is a hormone produced by your thyroid gland that plays a key role in regulating metabolism and energy levels.
["Your doctor may check your T4 level to assess thyroid function and help diagnose conditions like hypothyroidism or hyperthyroidism."]
Key facts at a glance
- LOINC
- 11062-7
- Short code
- T4 Alb Bnd SerPl-mCnc
- Synonyms
- T4 Alb Bnd SerPl-mCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 4.5
- Ref high
- 12
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 84436
- SNOMED
- 302345006
- 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?
Doctors order total T4 tests often when they suspect thyroid issues, such as when you have symptoms like fatigue, weight changes, or unexplained goiter. It may also be used as part of a routine thyroid function panel to monitor treatment for thyroid disorders.
What to Expect Before the Test
No special preparation is needed for this blood test. You may have fasting instructions depending on your doctor’s protocol, but generally, you can eat and drink as usual. A healthcare professional will draw blood from a vein in your arm.
What Happens During the Test?
A small needle is inserted into your arm to collect a blood sample. You may feel a brief pinch, but the process is quick. The blood is then sent to a lab for analysis using a sensitive immunoassay method to measure T4 levels accurately.
What the Results Mean
Results are interpreted by your healthcare provider based on your symptoms, medical history, and other lab tests. Abnormal levels may indicate thyroid dysfunction, but they often require additional testing to confirm a diagnosis.
Reference range
Adult: 4.5-12.0 μg/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: Understanding Your T4 Levels
Short name
Total T4
Frequently asked questions
What Are Common Questions About This Test?
Can I take my thyroid medication before the blood draw? If you take thyroid hormone replacement or medication, your doctor may advise timing it around the blood draw to avoid affecting results.
How often should I get this test? Frequency depends on your health status and treatment plan. Your doctor will determine how often to check your T4 levels based on your needs.
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 16, 2026. · Read our editorial policy