FREE T4 or Thyroxine

"This blood test measures the level of free thyroxine, one of the main hormones produced by the thyroid gland. It is essential when investigating symptoms such as persistent tiredness, unexplained weight gain or loss, sensitivity to cold or heat, hair thinning, or changes in mood. It is often used alongside TSH to provide a clearer picture of thyroid function.

Preparation: No fasting. High-dose biotin supplements may interfere; follow clinic advice."