All biomarkersCategory: Thyroid balance

Free thyroxine (T4L)

Free thyroxine (T4L) is the unbound, active form of the T4 hormone produced by the thyroid gland. T4 is converted to T3 in tissues and regulates metabolism, growth, and development. Free T4 levels are essential for assessing thyroid function and monitoring thyroid balance.

Understand your biology

Track your biomarkers with Lucis — personalised wellness insights and longitudinal tracking to build healthier habits.

View plans

Related biomarkers