Thyroid Cancer: Diagnosis

Approved by the Cancer.Net Editorial Board, 09/2023

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find the cause of a medical problem. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, cancer. They also do tests to learn if cancer has spread to another part of the body from where it started. If cancer has spread, it is called metastasis. Doctors may also do tests to learn which treatments could work best.

For most types of cancer, a biopsy is the only sure way for the doctor to know if an area of the body has cancer. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis.

How thyroid cancer is diagnosed

There are different tests used for diagnosing thyroid cancer. Not all tests described here will be used for every person. Your doctor may consider these factors when choosing a diagnostic test:

  • The type of cancer suspected

  • Your signs and symptoms

  • Your age and general health

  • The results of earlier medical tests

The following tests may be used to diagnose thyroid cancer:

  • Physical examination. The doctor will feel the neck, thyroid gland, throat, and lymph nodes (the small, bean-shaped organs that help fight infection) in the neck for unusual growths or swelling. If surgery is recommended, the larynx may be examined at the same time with a laryngoscope, which is a thin, flexible tube with a light.

  • Blood tests. There are several types of blood tests that may be done during diagnosis and to monitor the patient during and after treatment. This includes tests called tumor marker tests. Tumor markers are substances found at higher-than-normal levels in the blood, urine, or body tissues of some people with cancer. Blood testing may include:

    • Thyroid hormone levels. As explained in the Introduction, thyroid hormones regulate a person’s metabolism. The doctor will use this test to find out the current levels of the thyroid hormones triiodothyronine (T3) and thyroxine (T4) in the body.

    • Thyroid-stimulating hormone (TSH). This blood test measures the level of TSH, a hormone produced by the pituitary gland near the brain. If the body is in need of thyroid hormone, the pituitary gland releases TSH to stimulate production.

    • Tg and TgAb. Thyroglobulin (Tg) is a protein made naturally by the thyroid as well as by differentiated thyroid cancer. After cancer treatment, there should be very low levels of thyroglobulin in the blood since the goal of treatment is to remove all thyroid cells. If Tg is rising after surgery and/or radioactive iodine, it may be a sign of more cancer. A tumor marker test may be done to measure the body’s Tg level before, during, and/or after treatment. There is also a test for thyroglobulin antibodies (TgAb), which are proteins produced by the body to attack thyroglobulin that occur in some patients. If TgAb is found, it is known to interfere with the results of the Tg level test.

    • Medullary type-specific tests. If medullary thyroid cancer (MTC) is a possibility, the doctor will order tumor marker tests to check for high calcitonin and carcinoembryonic antigen (CEA) levels. The doctor should also recommend a blood test to look for the presence of RET proto-oncogenes (see Risk Factors), particularly if there is a family history of MTC.

  • Ultrasound. An ultrasound creates a picture of the internal organs using sound waves. An ultrasound wand or probe is guided over the skin of the neck area. High-frequency sound waves create a pattern of echoes that show the doctor the size of the thyroid gland and specific information about any nodules, including whether a nodule is solid or a fluid-filled sac called a cyst.

  • Biopsy. The way to determine whether a nodule is cancerous or benign is through a biopsy. A biopsy is the only way to make a definite diagnosis, even if other tests can suggest that cancer is present. During biopsy, the doctor removes cells from the nodule that are then examined by a cytopathologist. A cytopathologist is a doctor who specializes in analyzing cells and tissue to diagnose disease. This test is often done with the help of an ultrasound (see above).

    A biopsy for thyroid nodules will be done in 1 of 2 ways:

    • Fine needle aspiration. This procedure is usually performed in a doctor’s office or clinic. It is an important diagnostic step to find out if a thyroid nodule is benign or cancerous. A local anesthetic may be injected into the skin to numb the area before the biopsy. The doctor inserts a thin needle into the nodule and removes cells and some fluid. The procedure may be repeated 2 or 3 times to get samples from different areas of the nodule. A report of the results of this test is created by the cytopathologist. The test results can come back as positive, meaning there are cancerous cells, or negative, meaning there are no cancerous cells. The test can also be undetermined, meaning it is not clear whether cancer is there.

    • Surgical biopsy. If the needle aspiration biopsy is not clear, the doctor may suggest a biopsy in which the nodule and possibly the affected lobe of the thyroid will be removed using surgery. Removal of the nodule alone is usually not recommended due to the potential to incompletely remove the potentially cancerous tumor without enough margins, which is an area of tissue around the nodule. This procedure is usually done under general anesthesia. It may also require a hospital stay.

  • Molecular testing of the nodule sample. Your doctor may recommend running laboratory tests on a tumor sample to identify specific genes, proteins, and other factors unique to the tumor. Genetic analysis of your thyroid nodule may allow you to understand the risk of the thyroid nodule being cancerous. Other genetic, protein, and molecular analysis of thyroid cancers can help determine your treatment options, including types of treatments called targeted therapy.

  • Radionuclide scanning. This test may also be called a whole-body scan. This scan will either be done using a very small, harmless amount of radioactive iodine I-131 or I-123, called a tracer. It is used most often to learn more about a thyroid nodule. In this test, the patient swallows the tracer, which is absorbed by thyroid cells. This makes the thyroid cells appear on the scan image, allowing the doctor to see differences between those cells and other body structures.

  • X-ray. An x-ray is a way to create a picture of the structures inside of the body, using a small amount of radiation. For instance, a chest x-ray can help doctors determine if the cancer has spread to the lungs.

  • Computed tomography (CT or CAT) scan. A CT scan creates a 3-dimensional picture of the inside of the body using x-rays taken from different angles. A computer combines these pictures into a detailed, cross-sectional view that shows any abnormalities or tumors. A CT scan can be used to measure the tumor’s size. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein or given as a pill to swallow.

    CT scans are often used in people with thyroid cancer to examine parts of the neck that cannot be seen with ultrasound (see above). Also, CT scans of the chest may be needed to look to see if thyroid cancer has spread to that area of the body. CT scans of the abdomen may be used to see if thyroid cancer has spread to the liver or other sites. Patients with the hereditary form (see Risk Factors) of MTC may be at risk for developing other types of endocrine tumors in the abdomen; these patients may also have a CT scan of the abdomen.

  • Positron emission tomography (PET) or PET-CT scan. A PET scan creates pictures of organs and tissues inside the body. A PET scan is usually combined with a CT scan (see above), called a PET-CT scan. But you may hear your doctor refer to this procedure just as a PET scan. A small amount of a radioactive sugar substance is injected into the patient’s body. This sugar substance is taken up by cells that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. However, the amount of radiation in the substance is too low to be harmful. A scanner then detects this substance to produce images of the inside of the body.

After diagnostic tests are done, your doctor will review the results with you. If the diagnosis is thyroid cancer, these results also help the doctor describe the cancer. This is called staging.

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the thyroid cancer. Use the menu to choose a different section to read in this guide.