Thyroid Uptake & Scan

What is a thyroid uptake and scan?

A thyroid uptake and scan is a diagnostic imaging test that healthcare providers use to assess the function of your thyroid. It’s a type of nuclear medicine imaging.

The test uses small amounts of radioactive materials called radiotracers and a special camera to show your thyroid’s size, shape and function. A thyroid uptake and scan can provide information that other, more common imaging tests — such as a thyroid ultrasound — can’t.

What is the difference between thyroid scan and uptake?

A thyroid scan and a thyroid uptake test are technically different procedures, but healthcare providers usually perform them together.

A thyroid uptake test is also known as a radioactive iodine uptake test (RAIU). It’s a nuclear medicine test that measures how much radioactive iodine your thyroid absorbs over a given time. A healthcare provider places a probe over your thyroid to measure the amount of radioactivity in your gland. Based on the amount, your provider can tell if your thyroid is overactive or underactive. A thyroid uptake test itself doesn’t involve imaging.

A thyroid scan does involve imaging. Using radiotracers, a special camera and a computer, your provider can see the shape, size and structure of your thyroid and where the overactive or underactive parts are within it.

Why would I need a thyroid uptake and scan?

Healthcare providers perform a thyroid uptake and scan for several reasons, including:

• To see if your thyroid is working properly. Providers usually recommend this test if you have a diagnosis of overactive thyroid (hyperthyroidism).
• To further assess the nature of a thyroid gland lump (nodule) after a thyroid ultrasound.
• To evaluate changes in your thyroid following medication use or surgery for hyperthyroidism.

Who performs a thyroid uptake and scan?

A radiologist who specializes in nuclear medicine imaging performs a thyroid uptake and scan.

How do a thyroid uptake and scan work?

A thyroid uptake and scan involve a safe, radioactive liquid (radiotracer) that a healthcare provider injects into one of your veins. In some cases, you may swallow it or inhale it as a gas. The radioactive liquid flows through your bloodstream, and your thyroid gland then absorbs it.

The radiotracer gives off gamma rays. In the thyroid uptake part of the process, a provider passes a gamma probe over your thyroid to detect how much radioactivity it gives off. This helps determine how well your thyroid is functioning.

During the thyroid scan, special cameras detect this radioactivity, and a computer creates detailed pictures of your thyroid. The overactive or abnormal areas of your thyroid will appear enlarged and “bright” in the image. These images provide information on how your thyroid looks and which areas, in particular, are abnormal.

How do I prepare for a thyroid uptake and scan?

It’s essential to tell your healthcare provider and radiologist if you’re pregnant, or think you might be pregnant, or are breastfeeding (chestfeeding) before undergoing this scan.

It’s also important to tell your provider about:

• Any recent illnesses you’ve had.
• Your medical conditions.
• Your allergies.
• Medications you’re taking.
• Whether you’ve had any procedures within the last two months that used iodine-based contrast material, such as IV iodine contrast/CT scan (computed tomography scan) contrast.

If you’re taking hyperthyroidism medications such as methimazole or propylthiouracil (PTU), your provider may give you instructions about when to stop taking them before the scan.

Your provider will let you know about anything else you need to do to prepare. They may tell you not to eat for several hours before the test. If you have any questions, don’t hesitate to ask them. Follow your provider’s instructions carefully.

What happens during a thyroid uptake and scan?

A thyroid uptake and a thyroid scan have different processes.

Thyroid uptake process

The steps of a thyroid uptake include:

1. A provider will give you radioactive iodine (a radiotracer) in liquid or pill form to swallow. The radiotracer will have little or no taste.
2. After four to six hours of swallowing the radiotracer, you’ll come back to the medical office. You’ll lie down on an exam table. A provider will pass a gamma probe over your neck to measure the amount of radioactivity your thyroid gives off.
3. They may have you come back again 24 hours after swallowing the radiotracer to get another measurement.

The scanning time with the gamma probe takes five minutes or less.

Thyroid scan process

The steps of a thyroid scan include:

1. A provider will give you an IV injection of a radiotracer (in most cases) or you’ll swallow it or inhale it as a gas.
2. After your thyroid has absorbed the radiotracer, you’ll lie on a moveable exam table with your neck extended backward.
3. A provider will position the medical camera over your neck and take a series of images at different angles. It’s important to remain still while the camera is taking pictures.
4. You may need to wait until the provider determines if they have enough images. Sometimes, the provider takes more pictures to clarify certain areas of your thyroid. There’s no need to worry if they need to take additional pictures.

The scanning time for a thyroid scan is around 30 minutes or less.

What happens after a thyroid uptake and scan?

Unless your provider tells you otherwise, you’ll be able to go back to your normal activities after the test. You should drink plenty of water to help your body flush out the radiotracer.

What are the risks and side effects of a thyroid uptake and scan?

As a thyroid uptake and scan uses a very small amount of radioactive liquid (radiotracer), your radiation exposure is low. Because of this, the benefits of the scan in assessing the function and health of your thyroid outweigh the very low radiation risk.

However, radiation exposure can affect a fetus if you’re pregnant or your baby if you’re breastfeeding (chestfeeding).

Other possible complications of this procedure include:

• Pain at the radiotracer injection site. This should resolve within a couple of days.
• Allergic reaction to the radiotracer. This is very rare, and the reaction is usually mild. The reaction isn’t to iodine itself but to the preparation containing iodine.

When should I know the results of the thyroid uptake and scan?

The timeline for receiving your results may depend on the reason for the thyroid uptake and scan and if your team needs a second opinion.

In general, a radiologist or other provider specially trained in nuclear scans will interpret the images and send a report to your healthcare provider who ordered the test. Your provider will then go over the results with you.

A note from Cleveland Clinic

A thyroid uptake and scan is a safe and helpful tool for assessing the function and health of your thyroid gland. If you have any questions about the procedure process, don’t be afraid to ask your healthcare provider. They’re available to help.