Thyroid-Stimulating Hormone (TSH)
hormone (TSH) blood test is used to check for
thyroid gland problems. TSH is produced when the
hypothalamus releases a substance called
thyrotropin-releasing hormone (TRH). TRH then triggers the
pituitary gland to release TSH. See pictures of the
thyroid gland and the
pituitary gland .
TSH causes the thyroid gland to make two hormones:
triiodothyronine (T3) and thyroxine (T4). T3 and T4 help control your body's
Triiodothyronine (T3) and
thyroxine (T4) are needed for normal growth of the brain, especially during the
first 3 years of life. A baby whose thyroid gland does not make enough thyroid
hormone (congenital hypothyroidism) may, in severe cases, be mentally retarded.
Older children also need thyroid hormones to grow and develop normally.
This test may be done at the same time as tests to measure T3 and T4.
Why It Is Done
A test for thyroid-stimulating hormone (TSH) is done to:
- Find out whether the thyroid gland is working
- An underactive thyroid gland (hypothyroidism) can cause symptoms such as weight
gain, tiredness, dry skin, constipation, a feeling of being too cold, or
frequent menstrual periods.
- An overactive thyroid (hyperthyroidism) can cause symptoms such as weight
loss, rapid heart rate, nervousness, diarrhea, a feeling of being too hot, or
irregular menstrual periods.
- Find the cause of an underactive thyroid gland
(hypothyroidism). TSH levels can help determine whether hypothyroidism is due
to a damaged thyroid gland or some other cause (such as a problem with the
pituitary gland or the hypothalamus).
- Keep track of treatment with
thyroid replacement medicine for people who have
- Keep track of thyroid gland function in people who
are being treated for hyperthyroidism. This treatment may include antithyroid
medicine, surgery, or radiation therapy.
- Double-check the diagnosis
of an underactive thyroid gland in a newborn (congenital
How To Prepare
Tell your doctor if you have had any
tests in which you were given radioactive materials or had X-rays that used
iodine dye within the last 4 to 6 weeks. Your test results may not be correct
if you have had iodine contrast material before having a thyroid-stimulating
hormone (TSH) test.
How It Is Done
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure to the site and then put on a