A thyroid-stimulating 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.
the thyroid gland to make two hormones: triiodothyronine (T3) and thyroxine (T4).
T3 and T4 help control your body's metabolism.
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.
out whether the thyroid gland is working properly.
An underactive thyroid
gland (hypothyroidism) can cause symptoms such as weight
gain, tiredness, dry skin, constipation, a feeling of being too cold, or frequent
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 hypothyroidism.
Keep track of thyroid
gland function in people who are being treated for hyperthyroidism. This treatment
may include antithyroid medicine, surgery, or radiation therapy.
the diagnosis of an underactive thyroid gland in a newborn (congenital hypothyroidism).
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
health professional drawing blood will:
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 alcohol.
the needle into the vein. More than one needle stick may be needed.
a tube to the needle to fill it with blood.
Remove the band from your arm
when enough blood is collected.
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
How It Feels
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight. You
may feel nothing at all from the needle, or you may feel a quick sting or pinch.
is very little chance of a problem from having a blood sample taken from a vein.
may get a small bruise at the site. You can lower the chance of bruising by keeping
pressure on the site for several minutes.
In rare cases, the vein may become
swollen after the blood sample is taken. This problem is called phlebitis. A warm
compress can be used several times a day to treat this.
hormone (TSH) blood test is used to check for thyroid gland problems.
The normal values
listed here-called a reference range-are just a guide. These ranges vary from lab
to lab, and your lab may have a different range for what's normal. Your lab report
should contain the range your lab uses. Also, your doctor will evaluate your results
based on your health and other factors. This means that a value that falls outside
the normal values listed here may still be normal for you or your lab.
Reasons you may not be able to have the test or why the results may
not be helpful include:
Taking medicine, such as corticosteroids, levodopa,
heparin, dopamine, or lithium (such as Lithobid).
Having had a recent X-ray
with iodine dye or test using radioactive materials.
Having severe stress
or a long-term (chronic) illness.
What To Think About
hormone (TSH) test is the best screening test for conditions that can affect the thyroid
The results of a TSH test should be considered along with the results
of thyroid hormone tests, especially thyroxine (T4) results. To learn more about T3
and T4 testing, see the topic Thyroid Hormone Tests.
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott
Williams and Wilkins.
Other Works Consulted
FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2010).
Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
ByHealthwise Staff Primary
Medical ReviewerE. Gregory Thompson, MD - Internal
Medicine Kathleen Romito, MD - Family Medicine Matthew I. Kim, MD - Endocrinology, Diabetes and Metabolism
This information does not replace the advice of a doctor.
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