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Thyroid hormone tests are blood tests that check how well the
thyroid gland is working. The thyroid gland makes
hormones that regulate the way the body uses energy.
gland is a butterfly-shaped gland that lies in front of your windpipe
(trachea), just below your voice box (larynx). The thyroid gland uses iodine
from food to make two thyroid
hormones: thyroxine (T4) and
triiodothyronine (T3). The thyroid gland stores these
thyroid hormones and releases them as they are needed.
hormones are needed for normal development of the brain, especially during the
first 3 years of life.
Intellectual disability may occur if a baby's thyroid gland
does not produce enough thyroid hormone (congenital
hypothyroidism). Older children also need thyroid
hormones to grow and develop normally, and adults need the hormones to regulate
the way the body uses energy (metabolism). The
United States Preventive Services Task Force
recommends that all newborns be tested for congenital hypothyroidism.footnote 1
Thyroid hormone blood tests include:
Thyroid hormone tests are done
Many medicines may change the results
of this test. Be sure to tell your doctor about all the nonprescription and
prescription medicines you take. If you are taking thyroid medicines, tell your
doctor when you took your last dose. Your doctor may instruct you to stop
taking thyroid medicines temporarily before having this test.
to your doctor about any concerns you have regarding the need for the test, its
risks, how it will be done, or what the results will mean. To help you
understand the importance of this test, fill out the
medical test information form (What is a PDF document?).
The health professional taking a sample
of your blood will:
A heel stick is used to obtain a blood
sample from a newborn. The baby's heel is pricked with a sharp instrument
(lancet) and several drops of blood are collected.
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.
A brief pain, like a sting or a pinch,
is usually felt when the lancet punctures the skin. Your baby may feel a little
discomfort with the skin puncture.
There is very little chance of a
problem from having blood sample taken from a vein.
There is very little chance of a
problem from a heel stick. A small bruise may develop at the site.
Thyroid hormone tests are blood tests
that check how well the
thyroid gland is working.
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.
Results are usually available within a few days.
measure free T4 (FT4) levels, but also may measure total thyroxine (T4) and T3
uptake (T3U). Results of these thyroid hormone tests may be compared to your
thyroid-stimulating hormone (TSH) results.
micrograms per deciliter (mcg/dL) or 152-292 nanomoles per liter (nmol/L) in newborns
6.4-13.3 mcg/dL (83-172 nmol/L) in babies and older children
5.4-11.5 mcg/dL (57-148 nmol/L) in adults
nanograms per deciliter (ng/dL) or 10-26 picomoles per liter (pmol/L)
105-245 ng/dL (1.6-3.8 nmol/L) in children ages 1-14
82-213 ng/dL (1.3-3.28 nmol/L) in adolescents ages 12-23
80-200 ng/dL (1.2-3.1 nmol/L) in adults
260-480 picograms per deciliter (pg/dL) or 4.0-7.4 pmol/L in adults
1.5-4.5 (index) in adults
Many conditions can change thyroid hormone levels.
Your doctor will talk with you about any abnormal results that may be related
to your symptoms and past health.
High thyroid hormone levels (hyperthyroidism) may be caused by:
Low thyroid hormone levels (hypothyroidism) may be caused by:
Reasons you may not be able to
have the test or why the results may not be helpful include:
U.S. Preventive Services Task Force (2008). Screening for congenital hypothyroidism: Reaffirmation recommendation statement. Available online: http://www.uspreventiveservicestaskforce.org/uspstf08/conhypo/conhyprs.htm. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
ByHealthwise Staff Primary Medical Reviewer Kathleen Romito, MD - Family Medicine E. Gregory Thompson, MD - Internal Medicine Specialist Medical Reviewer Adam Husney, MD - Family Medicine
Current as ofMay 3, 2017
Current as of:
May 3, 2017
Kathleen Romito, MD - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Adam Husney, MD - Family Medicine
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