The Free Triiodothyronine (Free T3) test is a laboratory test used to measure the level of free T3 hormone in the blood. T3 is one of the main hormones produced by the thyroid gland and plays an active role in regulating many body functions, including metabolism, growth, and tissue development. This test helps doctors diagnose and evaluate thyroid disorders such as hyperthyroidism or hypothyroidism. It is usually performed as part of a comprehensive evaluation of thyroid function and is often requested alongside the Thyroid Stimulating Hormone (TSH) test and the Total T3 test. The procedure involves drawing a blood sample from a vein, where the level of free T3 is measured in units such as picograms per milliliter (pg/mL). It is important to consult a doctor to understand and interpret the results accurately, as elevated or low levels may indicate certain health conditions that require further examination or treatment.