Thyroid hormones control how fast your body’s chemical functions work (your metabolic rate). Almost every cell in your body needs thyroid hormones. Among many other things, thyroid hormones help control:
There are 2 thyroid hormones:
Iodine is needed by your thyroid gland in order to make thyroid hormones. You need only a tiny amount of iodine. But if your thyroid gland doesn't get iodine, it won't make enough thyroid hormones (a condition called hypothyroidism).
The pituitary gland in your brain makes a hormone called TSH.
If your pituitary gland detects too little thyroid hormone in your blood, it puts out more TSH to stimulate your thyroid gland to make more thyroid hormones. If there's too much thyroid hormone in your blood, your pituitary puts out less TSH. Then your thyroid gland makes less thyroid hormone.
The main tests of your thyroid gland are:
Blood tests for the thyroid measure the level of:
A high TSH level usually means you don't have enough thyroid hormones. And a very low TSH level usually means you have too much.
Imaging tests include:
In a nuclear scan, doctors give you a tiny amount of radioactive iodine. Because your thyroid gland needs iodine, it collects the radioactive iodine. Doctors detect the radioactive iodine with a special camera. If your thyroid gland isn't working, it won't take up the iodine normally. The camera can also detect any small growths (nodules) on your thyroid. The scan doesn't use enough radiation to harm you.