Skip to main navigation Skip to main content Skip to footer For Medicare For Providers For Brokers For Employers Español For Individuals & Families: For Individuals & Families Medical Dental Other Supplemental Explore coverage through work How to Buy Health Insurance Types of Dental Insurance Open Enrollment vs. Special Enrollment See all topics Shop for Medicare plans Member Guide Find a Doctor Log in to myCigna
Home Knowledge Center Wellness Library Radioactive Iodine Uptake Test

Radioactive Iodine Uptake Test

Test Overview

A radioactive iodine uptake (RAIU) test uses a radioactive tracer and a special probe to measure how much tracer the thyroid gland absorbs from the blood. The test can show how much tracer is absorbed by the thyroid gland. The RAIU test often is done along with a thyroid scan, which shows if the tracer is evenly spread in the gland. This helps your doctor know if the thyroid gland is working properly. The radioactive tracer commonly used in this test is iodine.

A radioactive iodine uptake test is done to find problems with how the thyroid gland works, such as hyperthyroidism.

Why It Is Done

Why It Is Done

A radioactive iodine uptake (RAIU) test is done to:

  • Find the cause of an overactive thyroid gland (hyperthyroidism).
  • Plan treatment for hyperthyroidism.
  • Plan treatment for patients who have had thyroid cancer surgery.
How To Prepare

How To Prepare

Tell your doctor if you:

  • Take any medicines regularly. Be sure your doctor knows the names and doses of all your medicines. Your doctor will instruct you if and when you need to stop taking any of the following medicines that can change the RAIU test results:
    • Thyroid hormones
    • Antithyroid medicines
    • Medicines or supplements that contain iodine, such as iodized salt, kelp, cough syrups, multivitamins, and the heart medicine amiodarone
  • Are allergic to any medicines, such as iodine. But even if you are allergic to iodine, you will likely be able to have this test. That's because the amount used in the tracer is so small that your chance of an allergic reaction is very low.
  • Have ever had a serious allergic reaction (anaphylaxis) from any substance, such as the venom from a bee sting or from eating shellfish.

Before an RAIU test, blood tests may be done to measure the amount of thyroid hormones (TSH, T3, and T4) in your blood.

Follow your doctor's instructions about not eating before the test. Your doctor may ask you to eat a low-iodine diet.

For an RAIU, you will swallow a dose of radioactive iodine. Iodine can be taken as a capsule or a fluid 4 to 24 hours before the test. Iodine has little or no taste.

Just before the test, you will remove your dentures (if you wear them) and all jewelry or metal objects from around your neck and upper body.

How It Is Done

How It Is Done

A radioactive iodine uptake (RAIU) test is done in the nuclear medicine section of a hospital's radiology department.

For this test, you will lie on your back with your head tipped backward and your neck extended. It's important to lie still during this test. A special machine is placed over your thyroid gland to measure the amount of tracer absorbed by the thyroid gland. This isn't an X-ray machine—it's a scanner that detects the radiation given off by the tracer. This test takes about 10 minutes. It's done 3 to 6 hours after you are given the tracer. Another scan may be done in 24 hours.

After an RAIU test, you can do your regular activities.

How It Feels

How It Feels

You may find it uncomfortable to lie still with your head tipped backward.

Risks

Risks

Anytime you're exposed to radiation, there's a small chance of damage to cells or tissue. That's the case even with the low-level radioactive tracer used for this test. But the chance of damage is very low compared with the benefits of the test.

Most of the tracer will leave your body through your urine or stool within a day. So be sure to flush the toilet right after you use it, and wash your hands well with soap and water. The amount of radiation in the tracer is very small. This means it isn't a risk for people to be around you after the test.

This test is not done for pregnant women because of the chance of exposing the baby (fetus) to radiation. This test is also not recommended for breastfeeding women or young children.

Results

Results

Radioactive thyroid scan and radioactive iodine uptake test (RAIU)

Normal:

The amount of radioactive tracer in the thyroid gland is normal. An RAIU test measures the amount of tracer taken up by the thyroid gland at certain times after the tracer is given. The measured amount of radioactive tracer in the thyroid gland at each one of these times is at normal levels.

Abnormal:

The test shows either more or less uptake of tracer than normal in the thyroid gland. If hyperthyroidism is present, abnormal test results may mean certain conditions are present.

  • A low uptake of tracer by the thyroid gland may mean that hyperthyroidism is caused by inflammation of the thyroid gland (thyroiditis), taking too much thyroid medicine, or another rare condition.
  • A high uptake of tracer spread evenly in the thyroid gland may mean that hyperthyroidism is caused by conditions such as Graves' disease.

This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Learn how we develop our content.

© 1995-2022 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

Related Links

Medical Tests: Questions to Ask the Doctor

<cipublic-spinner variant="large"><span>Loading…</span></cipublic-spinner>

Page Footer

I want to...

Get an ID card File a claim View my claims and EOBs Check coverage under my plan See prescription drug list Find an in-network doctor, dentist, or facility Find a form Find 1095-B tax form information View the Cigna Glossary Contact Cigna

Audiences

Individuals and Families Medicare Employers Brokers Providers

Secure Member Sites

myCigna member portal Health Care Provider portal Cigna for Employers Client Resource Portal Cigna for Brokers

Cigna Company Information

About Cigna Company Profile Careers Newsroom Investors Suppliers Third Party Administrators International Evernorth

 Cigna. All rights reserved.

Privacy Legal Product Disclosures Cigna Company Names Customer Rights Accessibility Non-Discrimination Notice [PDF] Language Assistance [PDF] Report Fraud Sitemap

Disclaimer

Individual and family medical and dental insurance plans are insured by Cigna Health and Life Insurance Company (CHLIC), Cigna HealthCare of Arizona, Inc., Cigna HealthCare of Illinois, Inc., and Cigna HealthCare of North Carolina, Inc. Group health insurance and health benefit plans are insured or administered by CHLIC, Connecticut General Life Insurance Company (CGLIC), or their affiliates (see a listing of the legal entities  that insure or administer group HMO, dental HMO, and other products or services in your state). Accidental Injury, Critical Illness, and Hospital Care plans or insurance policies are distributed exclusively by or through operating subsidiaries of Cigna Corporation, are administered by Cigna Health and Life Insurance Company, and are insured by either (i) Cigna Health and Life Insurance Company (Bloomfield, CT); (ii) Life Insurance Company of North America (“LINA”) (Philadelphia, PA); or (iii) New York Life Group Insurance Company of NY (“NYLGICNY”) (New York, NY), formerly known as Cigna Life Insurance Company of New York. The Cigna name, logo, and other Cigna marks are owned by Cigna Intellectual Property, Inc. LINA and NYLGICNY are not affiliates of Cigna.

All insurance policies and group benefit plans contain exclusions and limitations. For availability, costs and complete details of coverage, contact a licensed agent or Cigna sales representative. This website is not intended for residents of New Mexico.

Selecting these links will take you away from Cigna.com to another website, which may be a non-Cigna website. Cigna may not control the content or links of non-Cigna websites. Details