Alternate Names: Thyrotropin; Thyroid stimulating hormone
How 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: The health care provider may advise you to withhold drugs that may affect the test (see "special considerations").
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 experience, 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 It Feels: 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.
Risks:
- 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
Why Performed: TSH is measured to differentiate primary versus secondary hyperthyroidism or hypothyroidism. Primary hypothyroidism, for example, results from decreased production of T3 and T4 by the thyroid gland in spite of normal or increased stimulation by TSH. Secondary hypothyroidism results from decreased production of T3 and T4 as a result of decreased secretion of TSH from the pituitary gland.
TSH is secreted by the pituitary and stimulates secretion of T4 and T3 from the thyroid gland. TSH is, itself, stimulated by TRH, which is released by the hypothalamus. T3 and T4 feedback inhibit the release of both TSH and TRH in normal people.
Normal Values: 0.2 to 4.7 mcU/ml
Note: mcU/ml = microunits per milliliter
Abnormal Results: Greater-than-normal levels may indicate:
Lower-than-normal levels may indicate:Additional conditions under which the test may be performed:
Cost:
Special Considerations: Drugs that can increase TSH measurements include antithyroid medications, lithium, and potassium iodide.
Drugs that can decrease TSH measurements include aspirin, dopamine, heparin, and corticosteroids.
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.
