Definition of T3RU test:

The T3RU test measures the level of proteins that carry thyroid hormone in the blood.

How the test is performed:

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to prepare for the test:

Your health care provider will instruct you, if necessary, to stop taking drugs that may interfere with the test.

Drugs that can increase T3RU values include:

• Anabolic steroids
• Heparin
• Phenytoin
• Salicylates (high dose)
• Warfarin

The following can increase thyroxin binding globulin (TBG) levels:

• Androgens (male hormones)
• Serious illness
• Kidney disease

Drugs that can decrease T3RU values include:

• Antithyroid medications
• Birth control pills
• Clofibrate
• Estrogen
• Thiazides

Pregnancy can also decrease T3RU levels.

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:

This test is done as part of an evaluation of thyroid function. Your doctor may order this test if you have signs of a thyroid disorder. Thyroid function is complex and depends on the action of many different hormones, including thyroid-stimulating hormone (TSH), T3, and T4.

This test helps estimate the availability of thyroxin binding globulin (TBG). This is the protein that carries most of the T3 and T4 in the blood. The higher the level of TBG , the lower the value of T3RU. A higher T3RU value means less TBG is available, possibly as a result of hyperthyroidism.