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Endocrine glands
Endocrine glands
Pituitary and TSH
Pituitary and TSH

TSH
Definition:
A test that measures the amount of the hormone TSH in the blood.

Alternative Names:
Thyrotropin; Thyroid stimulating hormone

How the test is performed:
Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the 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. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
How to prepare for the test:

Adults: No special preparation is usually necessary

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel:
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:

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:

0.2 to 4.7 mcU/ml

Normal values depend on the individual assay

Note: mcU/ml = microunits per milliliter
What abnormal results mean:
Greater-than-normal levels may indicate: Lower-than-normal levels may indicate:

What the risks are:
  • 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:

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.
Review Date: 3/3/2002
Reviewed By: Mary D. Ruppe, Division of Endocrinology and Metabolism, Johns Hopkins Hospital, Baltimore, MD. Review provided by VeriMed Healthcare Network
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