First, a physician will take the patient’s medical history and perform a complete physical examination. During the exam, the physician will inspect the size and firmness of the patient’s thyroid and examine any enlarged lymph nodes in the neck. The patient may also be asked to tip their head back, take a drink of water and swallow. The physician then watches the area of the thyroid gland carefully because swallowing may make a thyroid nodule or enlarged thyroid gland more apparent. The physician may also feel (palpate) the thyroid gland as the patient swallows to try to detect nodules. If the physician suspects thyroid cancer, a biopsy of the area may be ordered.

A fine needle aspiration (FNA) biopsy is a type of biopsy that may be ordered to determine if a thyroid nodule is cancerous. It can be used to determine whether other tests or surgery are needed. In this procedure, a thin needle and a syringe are used to remove cells and fluid from the nodule. The process is usually repeated two or three times to collect samples from different areas of the nodule. The test should be performed on all nodules that can be felt. In some cases, FNA is used in combination with ultrasound imaging to help guide the needle into nodules that are too small to be felt.

The cells are examined under a microscope to determine whether the nodule is malignant (cancerous) or benign (noncancerous). According to the American Cancer Society (ACS), approximately one in 20 FNA thyroid tests show cancer and between 60 percent and 80 percent clearly show the tumor is benign. When the findings are inconclusive, and test results cannot be classified as benign or malignant, the nodules are classified as “suspicious” or “atypical.” In such cases, additional tests such as a surgical biopsy may be ordered. This is particularly common when the physician suspects cancer.

After a diagnosis of cancer has been confirmed, the disease will be staged. Staging is the process of determining how far the cancer has spread and is necessary to determine the most effective course of treatment.  Additional tests that may be performed to classify, stage and monitor thyroid cancer include:

• Thyroid scan. In this procedure, a small amount of radioactive iodine or technetium is taken by mouth or injected into a patient’s vein. The chemicals then concentrate in the thyroid gland. A special camera is then placed in front of the patient’s neck to measure the amount of radiation in the thyroid gland. Although this test is not useful in diagnosing thyroid cancer, it may be used to determine how far the cancer has spread.
  
  
• Ultrasound. This procedure uses high-frequency sound waves to produce images of the body. As the waves bounce off the thyroid tissue, the echo patterns are translated by a computer, and an image of the thyroid gland is created. This test may be used to determine the number and size of thyroid nodules, although it is less useful for diagnosis because benign and malignant nodules cannot be distinguished in ultrasound images.  
  
  
• Computed axial tomography (CAT) scan. Also known as a computed tomography (CT) scan, this test allows for multiple x-rays to be taken from different angles around the patient. The "slices" or cross–sectional images of the patient’s body are analyzed by a computer. Frequently after the first set of images is taken, the patient receives an intravenous (I.V.) injection of a contrast medium (dye) to better outline body parts. Then a second set of images is taken. CAT scans may be used to reveal tumors within the thyroid gland, and to determine if the cancer is growing or has spread.

• Magnetic resonance imaging (MRI). A powerful magnetic field creates images of structures and organs within the body allowing a computer to produce very clear cross-sectional or three-dimensional images. As with CAT scans, a contrast medium may be injected in the patient to improve the quality of the images. MRI tests may be used to reveal tumors within the thyroid gland and to determine if the cancer is growing or has spread.
  
  
• Octreotide scan. This procedure, which uses a radioactively tagged hormone, may be ordered to assess the spread of medullary thyroid carcinoma (MTC).
  
  
• Blood tests. A thyroid-stimulating hormone (TSH) blood test may be ordered to asses the overall condition of the thyroid gland. When medullary thyroid carcinoma (MTC) is suspected, a blood calcitonin test may be ordered to help confirm its presence. Other blood tests may be used after surgical treatment to determine if the cancer is still present or is recurring.  may be measured to determine if the cancer is still present or is coming back.