In order to diagnose thyroid cancer, your doctor will ask about your medical history and do a physical exam. Thyroid cancer is most often found during a routine physical exam.

If you have a lump or nodule in your thyroid, your doctor may order a CT scan or an ultrasound to get a better look at your thyroid. If your doctor thinks that the lump or nodule could be cancerous, he or she will do a biopsy of the thyroid gland. A biopsy involves removing a piece of your thyroid, often through a needle. This test is a simple procedure that can be done in your doctor's office.

You may also have certain blood tests.

• Serum thyroglobulin level. Thyroglobulin levels are usually high in people who have thyroid cancer, but your thyroglobulin level can be high even if you don't have cancer.
• Serum calcitonin. If you have medullary thyroid cancer (MTC), your calcitonin level may be high.
• Carcinoembryonic antigen (CEA). This test helps predict how well treatment may work. If your CEA is high, you may have medullary thyroid cancer, which is harder to treat than other types of thyroid cancer.

Other tests may be done before, during, or after your treatment for thyroid cancer.

• Radioactive iodine scans help determine whether thyroid cancer has spread beyond the thyroid gland. These scans are done after surgery to remove the gland.
• Thyroid ultrasound is a safe and simple way to find out whether a thyroid nodule is solid or fluid-filled (cystic). It can also detect multiple thyroid nodules.
• A chest X-ray may help identify thyroid cancer that has spread to the lungs. This is not common.
• A CT scan of the liver may be done to check for any spread of cancer to the liver. This is not common.

In rare cases, when thyroid cancer has significantly spread, an MRI or a PET scan may be done.

If you have medullary thyroid cancer (MTC), a CT scan of the chest and belly and a bone scan may also be needed.

Early Detection

The U.S. Preventive Services Task Force does not think there is enough evidence to recommend screening tests for thyroid cancer.³ Screening tests look for a certain health problem before any symptoms appear. Talk to your doctor about whether you need to be screened for thyroid cancer.

People who have a family history of medullary thyroid cancer (MTC) may want to have a genetic test to look for a gene change called an RET mutation. Before you have the test, it is a good idea to talk with a genetic counselor. He or she can help you understand what your test results may mean.