Diagnosis is the process of finding the cause of a health problem. The process of diagnosis may seem long and frustrating, but it is important for the doctor to rule out other reasons for a health problem before making a cancer diagnosis. Diagnostic tests for thyroid cancer are usually done when:
- the symptoms of thyroid cancer are present, such as lump in the front of the neck
- the doctor suspects thyroid cancer after talking with a person about their health and completing a physical examination
- an ultrasound or CT scan of the neck suggests a problem with the thyroid
Many of the same tests used to initially diagnose cancer are used to determine the stage (how far the cancer has progressed). Your doctor may also order other tests to check your general health and to help plan your treatment. Tests may include the following.
Medical history and physical examination
The medical history is a record of present symptoms, risk factors and all the medical events and problems a person has had in the past. The medical history of a person’s family may also help the doctor to diagnose thyroid cancer.
In taking a medical history, the doctor will ask questions about:
- the person’s general health and any health problems or concerns
- a personal history of
- prior radiation therapy to the neck area, especially as a child
- benign thyroid conditions
- inherited conditions that may increase the risk of thyroid cancer
- a family history of
- thyroid cancer
- other cancers
- inherited conditions that may increase the risk of thyroid cancer
- signs and symptoms that may suggest thyroid cancer
A physical examination allows the doctor to look for any signs of thyroid cancer. During a physical examination, the doctor may:
- feel the neck, thyroid and lymph nodes in the neck for swelling or nodules (abnormal areas or growths)
- check the throat for swelling
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Blood tests
The doctor may order a number of blood tests when assessing a person for thyroid cancer. Although these tests cannot confirm the presence of thyroid cancer, they provide information about how the thyroid gland is functioning and the person’s general health.
- thyroid stimulating hormone –TSH (thyrotropin) levels are usually normal in people with thyroid cancer. Checking the level helps the doctor determine how well the thyroid gland is functioning.
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Tumour marker tests
Tumour markers are substances – usually proteins – in the blood that may indicate the presence of thyroid cancer. Tumour marker tests are used to check a person’s response to cancer treatment, but they can also be used to diagnose thyroid cancer. Tumour markers that may be measured are:
- carcinoembryonic antigen (CEA) – CEA levels may be increased in medullary thyroid cancer.
- thyroglobulin – Thyroglobulin levels cannot diagnose cancer, but they are used in follow-up after treatment to see if the cancer has come back. The doctor may order an initial thyroglobulin level while trying to diagnose thyroid cancer so it can be compared to levels after treatment.
- calcitonin – The doctor usually checks the calcitonin level in the blood if medullary thyroid cancer is suspected. Calcitonin blood levels will be checked after treatment for medullary thyroid cancer to look for possible return of the cancer.
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Blood chemistry tests
Blood chemistry tests measure certain chemicals in the blood. They show how well certain organs are functioning and can also be used to detect abnormalities. They may be used to help stage thyroid cancer.
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Ultrasound
Ultrasound uses high-frequency sound waves to make images of structures in the body. Ultrasound cannot distinguish between benign and malignant nodules in the thyroid, but it can be used to:
- detect whether a lump is solid or cystic (filled with fluid)
- detect multiple thyroid nodules when only one can be felt
- monitor a suspicious nodule
- guide a biopsy needle into a thyroid nodule
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Biopsy
During a biopsy, cells are removed from the body so they can be tested in a laboratory. The pathology report from the laboratory will confirm whether or not cancer cells are present in the sample. A biopsy is the only definitive way to diagnose thyroid cancer. The biopsies that could be used for thyroid cancer are:
- fine needle aspiration (FNA) biopsy
- If the nodule isn't big enough to be felt, ultrasound may be used to guide the needle into the nodule.
- A number of samples may be taken from different areas of the nodule to ensure that the entire nodule has been examined.
- If the person has more than one nodule, samples may be taken from each one, depending on the size and appearance of the nodules.
- surgical biopsy
- This type of biopsy may be done if:
- an FNA could not be done
- the doctor couldn’t obtain enough cells during the FNA for a proper microscopic examination
- it was difficult for the pathologist to make a definite diagnosis from the FNA sample
- there were multiple nodules in the thyroid gland and it was too difficult to obtain FNA samples from each of them
- The entire thyroid nodule and possibly the affected lobe of the thyroid will be removed.
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Laryngoscopy
Laryngoscopy is done when the doctor wants to see if the thyroid lump is pressing on the larynx (voice box). People often have a hoarse voice if there is pressure on the larynx. A laryngoscopy allows the doctor to look at the vocal chords inside the throat using a flexible tube with a light and lens on the end (a laryngoscope).
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Computed tomography (CT) scan
A CT scan uses special x-ray equipment to make 3-dimensional and cross-sectional images of organs, tissues, bones and blood vessels inside the body. A computer turns the images into detailed pictures. It may be used to:
- help determine the location and size of the thyroid tumour (although ultrasound has become the preferred imaging test for this purpose)
- check organs and surrounding tissues for any spread of the cancer
- check lymph nodes surrounding the thyroid for spread of the cancer (if the lymph nodes are enlarged)
- precisely guide a biopsy needle into areas where the cancer is thought to have spread
A CT scan can detect cancer that has spread and developed into tumours in others parts of the body. It cannot detect cancer cells that have spread but have not yet developed into tumours (microscopic spread).
Sometimes intravenous contrast medium is used with a CT scan to provide a more detailed image. The contrast may sometimes not be used if it is suspected that the person has a differentiated thyroid cancer because it can interfere with radioactive iodine scans and treatment.
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Magnetic resonance imaging (MRI)
MRI uses powerful magnetic forces and radio-frequency waves to make cross-sectional images of organs, tissues, bones and blood vessels. A computer turns the images into 3-dimensional pictures. It may be used to:
- check for cancer in the thyroid gland (although ultrasound has become the preferred imaging test for this purpose)
- check if the cancer has spread to other tissues such as the lymph nodes, brain, spine or abdominal organs
MRI is expensive to perform and may not be as available as other imaging tests at every centre.
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Positron emission tomography (PET) scan
A PET scan uses radioactive materials (radiopharmaceuticals) to detect changes in the metabolic activity of body tissues and help find areas of active cancer cells. A computer analyzes the radioactive patterns and makes 3-dimensional colour images of the area being scanned. It may be used to:
- help find the cancer or see if it has recurred if other tests are negative but the doctor still suspects that the cancer is present
- help find metastatic spread in people whose thyroid cancer does not take up the radioactive iodine used in CT scans
PET scans are expensive to perform and may not be as readily available as other imaging tests in certain centres.
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Radioactive iodine scan
A radioactive iodine scan is also called a radionuclide scan or radioisotope scan. When it is used to examine the thyroid gland, it may be called a thyroid scan. A radioactive iodine scan uses a radioactive material (called an isotope) to highlight the structure of an organ. The radiation given off from the isotope is picked up by a scanning device to form a picture of the organ.
Radioactive iodine is the isotope used to detect nodules in the thyroid. These nodules are described as cold or hot nodules.
- Cold nodules absorb less radioactive iodine than the surrounding thyroid tissue. They may also be called hypofunctioning nodules. Most cold nodules are benign, although some may be cancerous.
- Warm or hot nodules absorb more radioactive iodine than the surrounding thyroid tissue. They may also be called hyperfunctioning nodules. Hot nodules are usually benign.
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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 may be done to see if the cancer has spread to the lungs.
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Bone scan
A bone scan uses radioactive materials (radiopharmaceuticals) that will gather in the bones and a computer to create a picture of the bones. It may be used to see if the thyroid cancer has spread to the bones.
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See a list of questions to ask your doctor about diagnostic tests.