MedlinePlus Medical Encyclopedia: TSH

Skip navigation


Medical Encyclopedia
Other encyclopedia topics:	A-Ag Ah-Ap Aq-Az B-Bk Bl-Bz C-Cg Ch-Co Cp-Cz D-Di Dj-Dz E-Ep Eq-Ez F G H-Hf Hg-Hz I-In Io-Iz J K L-Ln Lo-Lz M-Mf Mg-Mz N O P-Pl Pm-Pz Q R S-Sh Si-Sp Sq-Sz T-Tn To-Tz U V W X Y Z 0-9

TSH

Contents of this page:
Illustrations Alternative names Definition How the test is performed How to prepare for the test How the test will feel	Why the test is performed Normal Values What abnormal results mean What the risks are Special considerations

Illustrations

Endocrine glands

Pituitary and TSH

Alternative names Return to top

Thyrotropin; Thyroid stimulating hormone

Definition Return to top

TSH is a test that measures the amount of the hormone TSH in the blood.

How the test is performed Return to top

Adult or child:
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to fill with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. The tourniquet is then removed to restore circulation. After blood has been collected the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

How to prepare for the test Return to top

No special preparation is usually necessary.

Infants and children:
The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For general information regarding how you can prepare your child, see the following topics:

Infant test or procedure preparation (birth to 1 year)
Toddler test or procedure preparation (1 to 3 years)
Preschooler test or procedure preparation (3 to 6 years)
Schoolage test or procedure preparation (6 to 12 years)
Adolescent test or procedure preparation (12 to 18 years)

How the test will feel Return to top

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed Return to top

TSH is measured as a screening test for abnormal thyroid function.

TRH, a hormone produced in the hypothalamus, stimulates the pituitary gland to release TSH. TSH subsequently stimulates the thyroid to produce thyroid hormone, T3 and T4. These hormones feedback to the hypothalamus and pituitary to regulate the release of both TSH and TRH.

In certain diseases, this regulation pathway is altered leading to under- or over-production of thyroid hormone. When a thyroid disorder is suspected clinically, a TSH level is obtained as an initial test.

Normal Values Return to top

Normal values are from 0.4 to 4.0 mIU/L for those with no symptoms of an under- or over-active thyroid.

If you are being treated for a thyroid disorder, your TSH should be between 0.3 and 3.0 mIU/L. This means that you are being treated appropriately.

Some people with a TSH value over 2.5 mIU/L who have no signs (that is, no other abnormal thyroid function tests) or symptoms suggestive of an under-active thyroid may develop hypothyroidism sometime in the future. Anyone with a TSH above 2.5 mIU/L, therefore, should be followed very closely by a doctor.

Normal value ranges may vary slightly among different laboratories.

What abnormal results mean Return to top

Greater-than-normal levels may indicate:

Congenital hypothyroidism (cretinism)
Primary hypothyroidism
TSH-dependent hyperthyroidism
Thyroid hormone resistance

Lower-than-normal levels may indicate:

Hyperthyroidism
TSH deficiency

What the risks are Return to top

Excessive bleeding
Fainting or feeling lightheaded
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Multiple punctures to locate veins

Special considerations Return to top

Drugs that can affect TSH measurements include: antithyroid medications, lithium, potassium iodide, amiodarone, dopamine and prednisone.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Update Date: 2/2/2004

Updated by: Tarun Jain, M.D., Endocrinology & Infertility Division, Brigham and Women's Hospital, Boston, MA. Review provided by VeriMed Healthcare Network.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.