Thyroid hormone total (T4) with mass concentration measurement in serum/plasma
This test measures the amount of total thyroid hormone (T4) in your blood. T4 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
- 31144-9
- Short code
- T4 DBS-mCnc
- Synonyms
- T4 DBS-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
What Does This Test Measure?
Total T4 includes both active and inactive forms of thyroid hormone in your blood. It reflects the overall supply of thyroid hormone your body has available to use. The test helps assess whether your thyroid is producing enough hormone or if there’s an imbalance.
Why Might You Need This Test?
Doctors order total T4 tests to diagnose or monitor conditions like hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), or thyroid nodules. It’s also used during pregnancy, before starting thyroid hormone treatment, or if you have symptoms like fatigue, weight changes, or unexplained mood swings.
How Is the Test Performed?
A small blood sample is drawn from a vein in your arm. The blood is sent to a lab where it’s analyzed to measure the total T4 concentration. The result is compared to a reference range to determine if your levels are within normal limits.
What Are Common Symptoms to Watch For?
Symptoms of thyroid imbalances—such as fatigue, weight changes, hair loss, or changes in heart rate—may prompt a total T4 test. However, some people don’t experience symptoms until levels are severely out of range.
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: How Does This Test Help?
Short name
TOTAL T4 LEVEL
Frequently asked questions
How often will I need this test?
What do my results mean if they’re outside the normal range?
Can I eat or drink anything before the test?
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