How do they test for thyroid disease?

Function with lab te. The function of the gland can be tested with blood tests of thyroid hormone (t4 and T3 (liothyronine) and the pituitary response to function (tsh). The structure of the gland can be assessed with an ultrasound. Sometimes a radioisotope uptake (rai) and a radioiodide scan can test activity/structure.
Blood test . The TSH or thyroid stimulating hormone is the most accurate measure of thyroid function in most cases. It can be drawn at any time, don't have to be fasting.