the thyroid gland produce hormone that are found in the blood, thee hormone travel with the blood to carry nutrient and oxygen through out your body.

the test that is done to check on the thyroid is just a blood test... the blood test tells the doctor which hormones and how much, along with how much oxygen and nutrients are in your blood. the blood count numbers tell the doctor if your thyroid is normal or not.

if the blood test says your thyroid is normal then nothing needs to be done.

if the blood test says your thyroid is not normal then the blood test numbers tells the doctor which tests to do next like for example..

if your blood test says its lacking one hormone another blood test is done, then if that blood test says you are anemic then the doctor prescribes vitamins and an iron rich diet..and a test to look for things like ulcers in your digestion tract.

what ever your blood test shows tells the doctor what to look for next and what test to do.