An endocrinologist is a doctor who specialises in glands that produce hormones that regulate various bodily functions. This means that an endocrinologist uses a great deal of testing to do her job -- after all, the best way to measure whether a gland is performing properly is to test for a presence or lack of the chemical it is supposed to produce.
The most common disease an endocrinologist deals with is diabetes -- the body's inability to properly produce insulin. The major test for this condition is a blood sugar test; since insulin regulates blood sugar, an abnormally high blood sugar level is almost invariably indicative of diabetes. Endocrinologists therefore spend a great deal of their time administrating and analysing blood sugar tests.
Since endocrinologists deal with glands, one of the glands they deal with is the thyroid gland. A test they often perform is on lumps that appear on the thyroid, called goitre. To test for these, an endocrinologist performs an ultrasound, which is the use of high-frequency sound waves to map out the internal structure of the suspected goitre. As opposed to the blood sugar test, this is a physical test rather than a chemical test.
Endocrinologists also perform thyroid stimulating hormone (TSH) tests. The thyroid stimulating hormones regulate a wide variety of bodily functions, like your weight retention, memory, cholesterol levels and many other basic bodily functions.
The thyroid occasionally fails to produce enough hormones. When this happens, the pituitary gland produces TSH in order to compensate for it. So, a major test that endocrinologists carry out is the chemical test for TSH, the prevalence of which can indicate a thyroid disorder.