T3RU test Health Article

Definition

The T3RU test measures the level of thyroid hormone-binding proteins in the blood.

Alternative Names

Resin T3 uptake; T3 resin uptake; Thyroid hormone-binding ratio

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 discontinue drugs that may interfere with the test.

Drugs that can increase T3RU values include anabolic steroids, heparin, phenytoin, salicylates (high dose), and warfarin. Androgens (male hormones), serious illness, and kidney disease can also increase TBG levels.

Drugs that can decrease T3RU values include antithyroid agents, clofibrate, estrogen, birth control pills, and 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.