Definition: TSH (thyroid-stimulating hormone) is made by the pituitary gland and tells the thyroid how much hormone to make. When thyroid hormone is low, the pituitary makes more TSH. When it is high, the pituitary makes little or none. So a TSH test is a common first check of how well the thyroid is working.
TSH moves opposite to thyroid hormone. A high TSH usually goes with too little thyroid hormone (an underactive thyroid), and a low TSH with too much (an overactive thyroid). MedlinePlus says the test cannot show the cause, so other tests such as free T4, T3 and thyroid antibodies often follow an abnormal result.
In some cases an abnormal TSH can point to a pituitary problem rather than a thyroid one, though MedlinePlus says this does not happen often.
The Genotropin (somatropin) label says that in people with growth hormone deficiency, central (secondary) hypothyroidism may first appear or get worse during treatment, and that people on somatropin should have periodic thyroid function tests.
Thyroid hormone itself is a dosed medicine. MedlinePlus says people taking thyroid hormone have regular TSH tests to check they are on the right dose.
Each lab sets its own reference range, so read your result against the range printed on your own report, and talk with your clinician about what it means for you.
Read more on Dose Track: HGH guide · Logging lab results in Dose Track