Thyroid hormone total serum concentration (T4)
This test measures the amount of the primary hormone produced by your thyroid gland, which helps regulate metabolism, energy levels, and growth.
["Your doctor may check your total T4 level to assess thyroid function or monitor thyroid-related conditions."]
Key facts at a glance
- LOINC
- 83120-6
- Short code
- T4 SerPl IA-sCnc
- Synonyms
- T4 SerPl IA-sCnc
- 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
- Method
- ia
- 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 This Test Might Be Ordered
Your healthcare provider may request a total serum T4 test if you have symptoms like fatigue, weight changes, heat intolerance, or cold sensitivity. It could also be used during thyroid function evaluations, such as when checking for hypothyroidism or hyperthyroidism, or as part of routine thyroid monitoring.
What to Expect Before the Test
No special preparation is needed for this blood test. You may have fasting instructions depending on your clinic, but generally, you can eat and drink normally. Wear comfortable clothing and plan to stay for about 15 minutes while the blood is drawn.
What Happens During the Test
A healthcare professional will insert a small needle into a vein in your arm or hand to draw blood. You may feel a slight pinch, but it usually doesn’t cause significant discomfort. The blood sample is then sent to a lab for analysis.
What the Results Mean
Results are interpreted in relation to your overall health and symptoms. Low levels may suggest hypothyroidism, while high levels could indicate hyperthyroidism or other conditions. Your doctor will discuss the results with you and may recommend further testing if needed.
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.
◆Associated findings1
Short name
Total Serum T4
Frequently asked questions
How often should I get this test?
What are the common reference ranges for this test?
Can diet or medications affect my T4 test 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 16, 2026. · Read our editorial policy