This test screens and monitors the function of the thyroid.

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* Triiodothyronine (T3). Along with T4, this regulates your heart rate and body temperature.

* T3 resin uptake (RU). This measures how well a hormone called thyroxin-binding globulin is binding.

* Thyroxine (T4). Along with T3, this regulates your metabolism and how you grow.

* Thyroid-stimulating hormone (TSH). This helps regulate the levels of hormones your thyroid releases.