Thyroid Tests

What are thyroid tests?

Thyroid tests check to see if your thyroid gland works like it should. Your thyroid is a butterfly-shaped gland in your neck that sits just above your sternum (breastbone). It produces hormones that control several different body systems. It’s like a command center that manages how your body uses energy.

You might need a thyroid test if you have symptoms like fatigue, sluggishness, restlessness, irritability or unexplained weight changes. Thyroid tests can help diagnose thyroid diseases like:

• Hypothyroidism.
• Hyperthyroidism.
• Thyroiditis.
• Graves’ disease.
• Hashimoto’s disease.

Other names for thyroid tests include thyroid function tests and thyroid symptom tests.

Types of thyroid tests

There are several different types of thyroid tests, but they all fall under one of two categories:

• Thyroid blood tests check for hormones and proteins like antibodies and thyroglobulin. These tests can tell you if you have conditions like hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). There are several types of thyroid blood tests, including TSH, T3 and T4, and thyroid antibodies.
• Thyroid imaging tests help your provider find nodules (lumps) in your neck and determine whether they’re benign (noncancerous) or malignant (cancerous). Nuclear medicine imaging like thyroid uptake and scan tests fall under this category. (These tests involve injecting or swallowing a small amount of contrast material.)

How do thyroid blood tests work?

Thyroid blood tests measure certain hormones and antibodies in your blood. Too many or too few of these hormones or antibodies might mean that you have thyroid disease.

Providers use different blood tests to measure different things:

• TSH measures your thyroid-stimulating hormone. This is usually the first test most providers recommend. Your pituitary gland (part of your brain) makes TSH. It travels to your thyroid gland, stimulating it to produce thyroid hormones, T3 and T4.
• T3 (or free T3) measures the amount of triiodothyronine in your blood. This hormone is one of two main hormones that your thyroid makes.
• T4 (or free T4) measures the amount of thyroxine in your blood. Thyroxine is the other main type of hormone that your thyroid makes.
• Thyroid antibody tests tell your provider whether or not there are thyroid antibodies in your blood. The presence of thyroid antibodies might mean you have an autoimmune disorder like Graves’ disease or Hashimoto’s disease.

How to prepare for your thyroid blood test

Generally, you don’t need to do anything special prior to your test. You can eat and drink normally, unless your healthcare provider tells you otherwise.

What to expect during your thyroid blood test

During a thyroid blood test, a provider will take a sample of your blood and send it to a lab for analysis. Once the lab completes the testing, they’ll send the results to the provider who ordered it.

What to expect after your thyroid blood test

Your healthcare provider will discuss their findings with you. They might recommend additional testing if they need more information. They’ll tell you what your results mean and what comes next.

How do thyroid imaging tests work?

Thyroid imaging tests can give your provider more information about the size, shape and function of your thyroid gland. Providers might recommend imaging tests after you’ve already had thyroid blood tests.

Healthcare providers use different imaging tests for different reasons:

• Thyroid ultrasound uses sound waves to determine the shape, size and position of your thyroid gland. During this test, a provider places a handheld device against the skin on your neck. The device sends soundwaves through your body, and a receiver analyzes the soundwaves as they bounce off your thyroid. Providers use ultrasound to detect lumps (nodules) in your neck.
• Thyroid scans use computed tomography (CT) to look at the size and position of your thyroid gland. In most cases, your provider will use a contrast material to highlight areas of concern. Contrast materials block the amount of X-rays that go through your body and help get detailed pictures. This involves either an injection of radioactive iodine in your vein or a capsule that you swallow prior to the test. Sometimes providers take thyroid scans without contrast material, but it’s less common.
• Thyroid uptake tests tell your provider how well your thyroid works. Four to six hours before the test, you’ll swallow a small amount of radioactive iodine (in liquid or pill form). When you arrive for your appointment, you’ll sit in a chair while your provider places a gamma probe in front of your neck. (A gamma probe is a handheld device that measures how much iodine your thyroid takes up from your blood.) This procedure isn’t painful and it only takes a few minutes. In most cases, your provider will take another reading 24 hours later. If your thyroid takes up a large amount of iodine, it could mean you have hyperthyroidism or Graves’ disease. If your thyroid takes up a very small amount of iodine, it might indicate hypothyroidism or Hashimoto’s disease.

How to prepare for your thyroid imaging test

If your healthcare provider plans to use a contrast material, you might need to stop eating or drinking for a few hours before your procedure. Or, you might need to avoid kelp and other foods with a high iodine content.

Instructions will vary depending on your situation. Your provider will tell you if you need to make any special preparations.

What to expect after your thyroid imaging test

Your radiologist will send your imaging results to the provider that ordered the test. Once they review your scans, they’ll discuss their findings and recommendations with you.

If your scans show a lump on your neck, your provider may recommend a needle biopsy, also known as FNA (fine needle aspiration). This will tell them whether the lump is noncancerous or cancerous.

When should I know the results of my thyroid test?

Once your provider reviews your thyroid test results, they’ll call you to discuss them or schedule a follow-up office visit. In most cases, this process should only take a few days.

What blood tests show thyroid function?

Healthcare providers may run several blood tests to determine thyroid function. The two most common tests check your TSH (thyroid-stimulating hormone) and T4 or free T4 (thyroxine) levels.

Providers may also recommend a full thyroid blood test panel.

What is included in a full thyroid panel?

A full thyroid blood test panel measures the levels of these hormones and antibodies in your blood:

• TSH (thyroid-stimulating hormone).
• T3 or free T3 (tri-iodothyronine).
• T4 or free T4 (thyroxine).
• TPO (thyroid peroxidase antibodies), also known as microsomal antibodies.
• TG (thyroglobulin).
• TGAb (thyroglobulin antibodies).
• TSI (thyroid-stimulating immunoglobulin).

What happens if my TSH level is high?

If your TSH level is high, it might mean you have hypothyroidism. This means your thyroid gland doesn’t make enough thyroid hormone.

On the other hand, if your TSH is low, it could indicate hyperthyroidism. In this case, your thyroid gland makes too much thyroid hormone.

Your healthcare provider will discuss your results and tell you what they mean for you and your health.

What can affect thyroid test results?

There are certain things that can throw off your thyroid test results, including:

• Certain medications and supplements.
• The time between the last time you took your thyroid medication and when a provider draws your blood. (This is only a factor when you’re taking thyroid medication that contains T3.)
• Whether you ate before your test (only a factor with thyroid scans).
• Stress, including the effects on a non-thyroidal illness.

Do you have to fast for a thyroid test?

It depends on what type of test you have. Most healthcare providers don’t recommend fasting before a thyroid blood test. But for thyroid scans, especially those that require a contrast material, you may need to stop eating and drinking a few hours before your appointment.

Your healthcare provider will let you know if you need to fast or make other preparations before your thyroid test.

A note from Cleveland Clinic

Overactive and underactive thyroid can interfere with daily routines and hinder your quality of life. If you have symptoms of thyroid disease, a thyroid test can find out what’s causing them so your provider can recommend treatment.