These tests can't tell if you have thyroid cancer, but certain blood tests can help show if the thyroid is working as it should, which may help the doctor decide what other tests may be needed. "Routine" blood tests may be done during and after cancer treatment to check thyroid function or to help find out if the cancer may have returned. (CEA, Calcitonin Levels).
Other blood tests
You may have other blood tests as well. If you are scheduled for surgery, tests will be done to check your blood cell counts, to look for bleeding problems, and to check the function of your liver and kidneys.