• An elevated serum calcitonin after total thyroidectomy and a modified radical neck dissection for medullary
  carcinoma suggests persistent disease. Families of all patients with medullary carcinoma should also be
  screened. Serum calcitonin will be sampled after the intravenous injection of calcium and pentagastrin.
• CEA (carcinoembryonic antigen) levels are useful in predicting prognosis and discovering persistent disease in
  patients with medullary thyroid carcinoma.
• Blood tests, including serum alkaline phosphatase, are done to look for metastatic disease in the liver or bone.
  An elevated alkaline phosphatase level could suggest either liver or bone metastasis , leading to liver and bone
  scans. Selective venous catheterization for serum calcitonin is sometimes helpful for locating metastatic
  tumors.

Imaging 
• Images of the thyroid can be taken after injection of a radioactive iodine tracer or of technetium 99m. Because
  thyroid cancers do not generally take up as much iodine as normal thyroid tissue , a cancer appears as a cold
  area on a scan. Only about 20 percent of cold nodules are cancer, however, and "warm" nodules are rarely
  malignant . Though used extensively in the past to classify nodules as hot or cold, thyroid scans are used less
  and less because more information is provided by FNA.