UC San Diego Health
menu icon
search iconSearch
Health Library Explorer
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z Listings Contact Us
Click a letter to see a list of conditions beginning with that letter.
Click 'Topic Index' to return to the index for the current topic.
Click 'Library Index' to return to the listing of all topics.

Thyroid Cancer: Diagnosis

How is thyroid cancer diagnosed?

If your healthcare provider thinks you might have thyroid cancer, you will need certain exams and tests to be sure. Diagnosing thyroid cancer starts with your healthcare provider asking you questions. He or she will ask you about your health history, your symptoms, risk factors, and family history of disease. Your healthcare provider will also give you a physical exam.

What tests might I need?

You may have one or more of the following tests:

  • Blood tests

  • Imaging tests

  • Biopsy

Blood tests

A variety of blood tests will be used to see if your thyroid gland is working the way it should. These tests also help to check your overall health. These blood tests might include:

  • TSH (thyroid-stimulating hormone). This hormone is made by the pituitary gland. It tells the thyroid to make hormones called T3 and T4. This test can tell a lot about the overall activity of your thyroid gland. 

  • Thyroid hormone levels. This test is used to check the level of the thyroid hormones, T3 and T4, in your body.

  • Thyroglobulin. This is a protein made by the thyroid gland. The test measures this protein. 

  • Calcitonin. Levels of this hormone may be checked if your provider thinks you may have medullary thyroid cancer (MTC).

  • CEA (carcinoembryonic antigen). If MTC is suspected, this protein may be checked. MTC causes very high levels of CEA in the blood. 

Imaging tests

These tests can be used to look at the size of the thyroid gland. They can also be used to find the size and location of nodules or bumps that might be cancer.

  • Ultrasound. During this test, sound waves are used to look for thyroid cancer. The sound waves bounce off your thyroid and send back signals. A computer uses the signals to create an image of your thyroid. The image can show the size and location of any thyroid nodules and nearby swollen lymph nodes, which could mean cancer has spread to them. Ultrasound may be used to help guide a needle into the thyroid nodule or swollen lymph node to do a biopsy.

  • Radionuclide or radioiodine scan. A very small, harmless amount of radioactive iodine is swallowed or put in a vein. Over time, it’s absorbed by thyroid cells. This makes the thyroid cells easy to see on the scan that’s done with a special camera several hours later.

  • CT scan. This test uses X-rays to get detailed cross-sectional images of the body. It can be used to find the location and size of thyroid cancers.  It can also be used to help guide a biopsy needle into the area that's thought to be cancer. If MTC is suspected, a CT scan can be used to find other tumors in the body that are often linked to the MTC. 


A biopsy is a test to take small pieces of tissue from the body. The tissue (called a sample) is then looked at under a microscope. A biopsy is the only way to know for sure if a thyroid change is cancer.

During a biopsy, the healthcare provider will use an imaging test, like an ultrasound, to guide a very thin needle into your thyroid to take out cells and fluid. This is called a fine needle aspiration. This procedure can be done in the healthcare provider's office. The sample is sent to a pathologist, an expert who looks for changes in cells. The pathologist checks the cells and fluid under a microscope for any signs of cancer.

If the aspiration biopsy is not clear, it may be repeated. Or a surgical biopsy may be needed. This is when surgery is used to take out the nodule or the affected part of the thyroid gland to check for cancer cells.

Getting your test results

When your healthcare provider has the results of your biopsy, he or she will contact you with the results. Your provider will talk with you about other tests you may need if thyroid cancer is found. Make sure you understand the results and what follow-up you need.

Online Medical Reviewer: Hurd, Robert, MD
Online Medical Reviewer: Stump-Sutliff, Kim, RN, MSN, AOCNS
Date Last Reviewed: 5/1/2018
© 2020 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare provider's instructions.