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T4 test
Definition:
A T4 test measures the amount of the T4 hormone in the blood. T4 is produced by the thyroid gland. Alternative Names:
Thyroxine test
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How the test is performed:
Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell 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 band 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.
For an 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:
The health care provider may advise you to stop taking drugs that may affect the test (see "special considerations"). For infants and children: The preparation you can provide for this test depends on your child's age and experience. For specific information regarding how you can prepare your child, see the following topics:
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