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Thyroid Uptake Index (Radioiodine Uptake Test)

Published: August 9, 2026Updated: August 17, 2026

This test measures how well your thyroid takes up radioactive iodine, helping assess thyroid function and potential issues like hypothyroidism or hyperthyroidism.

Quick summary

["This test helps doctors evaluate thyroid uptake, which can guide treatment decisions for thyroid disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
3055-1
Short code
T3/T3 uptake index SerPl-Rto
Synonyms
T3/T3 uptake index SerPl-Rto
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 This Test Is Done

Your doctor may order this test if they suspect thyroid problems, such as an underactive (hypothyroidism) or overactive (hyperthyroidism) thyroid. It can also be used to check for thyroid nodules or after thyroid surgery.

How the Test Works

You’ll receive a small amount of radioactive iodine by mouth. After a set time (usually 24 hours), a scanner measures how much iodine your thyroid has absorbed. This helps determine if your thyroid is working normally or if there’s an abnormality.

Sample Collection

The test involves swallowing a tiny dose of radioactive iodine, which is harmless. No special preparation is needed, but you may be asked to avoid certain medications or foods that could interfere with results.

What to Expect During the Test

You’ll be monitored briefly after swallowing the iodine, but no further blood draws or procedures are required. You may experience mild radiation exposure, but it’s minimal and safe.

Reference range

Adult: 80-200 ng/dLN/A

Specimen: serum

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.

A low uptake may indicate hypothyroidism, thyroid nodules, or other thyroid issues, while a high uptake could suggest hyperthyroidism or other conditions. Results help guide treatment, such as medication adjustments or further testing.

Short name

Radioiodine Uptake Test

Frequently asked questions

How long does the test take?
The actual scan takes only a few minutes, but the total test duration is about 24 hours due to the waiting period for iodine uptake.
Is the radioactive iodine harmful?
No, the radioactive iodine used is very low-dose and poses minimal risk. You’ll be monitored closely, and radiation exposure is safe for healthy individuals.
Can I eat or drink normally before the test?
Yes, you can eat and drink normally, but avoid certain medications (like iodine supplements) that could affect results. Follow your doctor’s specific instructions.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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