Thyroid Hormone, Total Serum (T4) with Bromocresol Green (BCG) Colorimetric Method
This test measures the total amount of thyroid hormone (T4) in your blood using a specific chemical reaction to detect it.
["Total T4 helps assess your thyroid function and whether your body produces enough thyroid hormone."]
Key facts at a glance
- LOINC
- 3027-0
- Short code
- T4/T4BG SerPl
- Synonyms
- T4/T4BG SerPl
- 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?
Your healthcare provider may order this test if you have symptoms of thyroid issues, such as fatigue, weight changes, or unexplained mood swings. It can also be used to monitor thyroid hormone levels during treatment for conditions like hypothyroidism or hyperthyroidism.
What Does the Test Measure?
Total T4 is the combined form of active and inactive thyroid hormone in your blood. This test helps evaluate whether your thyroid gland is functioning normally or if there’s an imbalance.
How Is the Test Performed?
A blood sample is taken from a vein in your arm. The sample is sent to a lab where it undergoes a chemical process using bromocresol green to measure the total T4 concentration.
What Are Common Results?
Results are typically reported in micrograms per deciliter (µg/dL), but exact reference ranges may vary by lab. Your results will be compared to what is considered normal for your age and health status.
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: Total T4 is an important marker for thyroid function. Low levels may indicate hypothyroidism (underactive thyroid), while high levels may suggest hyperthyroidism (overactive thyroid) or other conditions affecting thyroid hormone metabolism. It is often used alongside other thyroid tests, such as TSH, for a complete evaluation.
Short name
Total T4 (Serum)
Frequently asked questions
What does a total T4 test measure?
How often should I get a total T4 test?
Can I eat or drink before this 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