Thyroid Uptake Index (Radioactive Iodine Uptake from Serum Thyroid Hormones)
This test measures how well your thyroid absorbs radioactive iodine from thyroid hormones in your blood. It helps assess thyroid function, especially in diagnosing conditions like hypothyroidism or hyperthyroidism.
["This test evaluates thyroid hormone uptake to guide thyroid function diagnosis and treatment planning."]
Key facts at a glance
- LOINC
- 3028-8
- Short code
- T4/T3 uptake index SerPl
- Synonyms
- T4/T3 uptake index SerPl
- Category
- coagulation
- 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
- 85610
- SNOMED
- 396252006
- 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 like fatigue, weight changes, or irregular heart rhythms, or if thyroid-related issues are suspected. It can also be used to monitor thyroid hormone replacement therapy.
What Does the Test Involve?
You’ll have a small amount of radioactive iodine injected into your bloodstream. After a set time (usually 24 hours), a special camera scans your thyroid to measure how much iodine it takes up. Your blood is also tested for thyroid hormones (T3 and T4) to calculate the uptake index.
What to Expect Before the Test
No special preparation is needed, but avoid iodine-containing supplements or foods (like seafood) for 24 hours before the test. Wear comfortable clothing and arrange for someone to drive you home afterward, as you’ll need to avoid contact with others due to radiation exposure.
What the Results Mean
The uptake index compares how much iodine your thyroid absorbs relative to the levels of thyroid hormones in your blood. Low uptake may suggest hypothyroidism, while high uptake could indicate hyperthyroidism or other thyroid disorders.
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.
Clinical Significance: This test helps diagnose and monitor thyroid disorders by assessing thyroid hormone metabolism and uptake efficiency. It complements other thyroid tests like TSH, free T4, and T3 levels to provide a full picture of thyroid function.
Short name
Thyroid Uptake Test
Frequently asked questions
What is a normal range for this test?
How long does it take to get results from this test?
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 17, 2026. · Read our editorial policy