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Thyroid cancer

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Diagnosis of thyroid cancer

Usually, diagnosing thyroid cancer begins when a routine test suggests a problem with the thyroid. Your doctor will ask you about any symptoms you have and do a physical exam. Based on this information, your doctor may refer you to a specialist or order tests to check for cancer or other health problems.

The process of diagnosis may seem long and frustrating. It’s normal to worry, but try to remember that other health conditions can cause similar symptoms as thyroid cancer. It’s important for the healthcare team to rule out other reasons for a health problem before making a diagnosis of thyroid cancer.

The following tests are commonly used to rule out or diagnose thyroid cancer. Many of the same tests used to diagnose cancer are used to find out the stage, which is how far the cancer has progressed. Your doctor may also order other tests to check your general health and to help plan your treatment.

Health history and physical exam

Your health history is a record of your symptoms, risk factors and all the medical events and problems you have had in the past. In taking a health history, your doctor will ask questions about a personal history of:

  • symptoms that suggest thyroid cancer
  • exposure to ionizing radiation, especially during childhood
  • non-cancerous thyroid conditions, including benign thyroid nodules, goitre and thyroiditis
  • a diet low in iodine

Your doctor may also ask about a family history of:

  • thyroid cancer and other cancers
  • hereditary conditions such as multiple endocrine neoplasia type 2 (MEN2)

A physical exam allows your doctor to look for any signs of thyroid cancer. During a physical exam, your doctor may:

  • feel the neck, thyroid and throat for any lumps, swelling or enlarged lymph nodes
  • do a laryngoscopy

Find out more about physical exam.

Blood tests

Blood tests measure certain cells or substances in the blood. They can help find abnormalities. Blood tests used to diagnose and stage thyroid cancer include the following.

Complete blood count (CBC) measures the number and quality of white blood cells, red blood cells and platelets. A CBC is done to check your general health.

Thyroid-stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3) and thyroid antibodies are measured to check how well the thyroid is working. TSH (also called thyrotropin) controls the amount of T4 and T3 in the blood. Higher or lower than normal levels of these hormones may mean the thyroid is not working properly. Thyroid antibodies may help diagnose the cause of thyroid problems. All of these tests are often done at the same time, which is called a thyroid panel.

Calcitonin is a hormone made by the thyroid. Doctors measure calcitonin if they think you might have medullary carcinoma.

Carcinoembryonic antigen (CEA) is a tumour marker. High levels of CEA may mean medullary carcinoma is present.

Find out more about blood tests.


An ultrasound uses high-frequency sound waves to make images of structures in the body. If doctors feel a lump in the neck, they can use ultrasound to check if there is just one or many nodules, as well as the size and shape of each nodule. Doctors also use ultrasound to find out if a nodule is solid or filled with fluid, has calcification (build-up of calcium) or other features that help make a diagnosis. They can also check tissues around the thyroid, including lymph nodes, to see if they are normal.

Doctors can also use ultrasound to guide a needle to a tumour to collect a biopsy sample.

Find out more about ultrasound.

Radioactive iodine tests

Doctors may use the following nuclear imaging tests to diagnose and stage thyroid cancer.

Radioactive iodine scan, or thyroid scan, uses radioactive material to examine the structure of the thyroid and look for any abnormal areas in other parts of the body. A small amount of radioactive iodine is swallowed or injected into a vein. This iodine is taken up, or absorbed, by thyroid cells (including thyroid cancer cells that have broken away from a tumour in the thyroid and spread to other parts of the body). A special camera and a computer create images of areas where the iodine builds up. A radioactive iodine scan is done to check if the nodule takes up large amounts of iodine (called a hyperfunctioning or hot nodule) compared to the rest of the thyroid. Most hyperfunctioning nodules are non-cancerous, or benign. The scan is also used to see if papillary, follicular or Hurthle cell carcinoma has spread outside of the thyroid.

Radioactive iodine uptake, or thyroid uptake, measures the amount of iodine taken up by the thyroid. This test is done using a special probe instead of a camera. It does not use imaging like the radioactive iodine scan. Doctors may do radioactive iodine uptake to see how well the thyroid is working, check for inflammation and find out what is causing an overactive thyroid (called hyperthyroidism).

Find out more about nuclear medicine imaging.


During a biopsy, the doctor removes tissues or cells from the body so they can be tested in a lab. The report from the lab will confirm whether or not cancer cells are present in the sample.

Fine needle aspiration (FNA) uses a very thin needle to remove a small amount of fluid or cells from a lump or mass. It is the most common biopsy used to check if there is cancer in a thyroid nodule. Sometimes the results of an FNA are not clear and the doctor can’t tell if a nodule is a benign thyroid nodule or follicular carcinoma. Depending on several factors, including risk factors and the results of other tests, the doctor may suggest doing a lobectomy (surgery to remove one side, or lobe, of the thyroid) to help make a diagnosis.

Core biopsy uses a hollow needle or probe to remove a piece of tissue so it can be examined under a microscope. It is sometimes used to check for cancer in a thyroid nodule.

Find out more about biopsy, fine needle aspiration (FNA) and core biopsy.

CT scan

A computed tomography (CT) scan uses special x-ray equipment to make 3-D and cross-sectional images of organs, tissues, bones and blood vessels inside the body. A computer turns the images into detailed pictures.

A CT scan may be used to check if thyroid cancer has spread to other parts of the body, such as lymph nodes in the neck.

Find out more about CT scan.


Magnetic resonance imaging (MRI) uses powerful magnetic forces and radiofrequency waves to make cross-sectional images of organs, tissues, bones and blood vessels. A computer turns the images into 3-D pictures.

MRI may be used to check if thyroid cancer has spread to other parts of the body.

Find out more about MRI.

Chest x-ray

An x-ray uses small doses of radiation to make an image of the body’s structures on film. A chest x-ray is done to see if thyroid cancer has spread to the lungs.

Find out more about x-ray.

PET scan

A positron emission tomography (PET) scan uses radioactive materials called radiopharmaceuticals to look for changes in the metabolic activity of body tissues. A computer analyzes the radioactive patterns and makes 3-D colour images of the area being scanned. A PET scan may be combined with a CT scan so they are done at the same time using the same machine (called PET-CT scan).

A PET scan or PET-CT scan is used to check if thyroid cancer has spread to other parts of the body. It is most useful when the thyroid cells do not absorb iodine.

Find out more about PET scan.

Questions to ask your healthcare team

Find out more about diagnosis. To make the decisions that are right for you, ask your healthcare team questions about diagnosis.


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