What role does FT3 play in Müdigkeit?

FT3 (free triiodothyronine) is the active form of thyroid hormone and plays a key role in energy metabolism. Low FT3 levels can cause fatigue, lethargy, and a slowed metabolism – classic signs of hypothyroidism. However, fatigue is non-specific; iron deficiency, vitamin B12 deficiency, sleep disorders, or psychological factors are also common causes. Measuring FT3 alone without TSH and fT4 is of limited value. Home tests for thyroid markers exist but provide only a screening hint. For persistent fatigue, a full thyroid panel (TSH, fT3, fT4, possibly antibodies) evaluated by a physician is recommended. The evidence linking FT3 to fatigue is based on physiological mechanisms and clinical practice, not on RCTs from the provided context. Caveat: self-interpretation of FT3 can lead to misdiagnosis; medical assessment is essential.