A thyroid-stimulating hormone (TSH) blood test is used to check for thyroid problems, such as hyperthyroidism or hypothyroidism. TSH controls the production of the 2 thyroid hormones: triiodothyronine (T3) and thyroxine (T4), which both regulate just about every function in your body, from temperature to mood, to metabolism
It works like this:
Your hypothalamus produces a substance called TRH
TRH triggers your pituitary gland to release TSH
TSH tells the thyroid to make T3 and T4
A TSH test measures how much TSH is being released by your pituitary gland. Based on the lab results, you will be able to determine a possible underlying cause of a thyroid problem – such as whether your thyroid isn’t working (not producing T3/T4) or if it working too much (overproduction of T3/T4). Too much or too little TSH production are both primary symptoms of thyroid disease.