This add-on measures the level of free triiodothyronine (T3) in your blood, the active thyroid hormone not bound to proteins. Free T3 plays a crucial role in regulating metabolism, energy levels, and temperature control. Imbalances in Free T3—even without obvious symptoms—can signal thyroid disorders such as hyperthyroidism or hypothyroidism, affecting everything from mood and weight to heart and digestive function.

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