A Thyroid Function Test (TFT) is a simple blood test that checks how well your thyroid gland is working by measuring three hormones: T3, T4 and TSH. The thyroid controls metabolism, energy, weight, heart rate and body temperature. This test helps diagnose underactive (hypothyroid) or overactive (hyperthyroid) thyroid, and is also used to monitor ongoing thyroid treatment. It is commonly advised for complaints such as weight change, hair fall, fatigue, menstrual irregularity, palpitations, infertility, or routine health checkups. No fasting or special preparation is needed.