What to watch with FT4 and Müdigkeit?

FT4 (free thyroxine) alone is insufficient to explain fatigue. The thyroid axis is complex: normal FT4 with elevated TSH may indicate subclinical hypothyroidism, while low FT4 with TSH >4 mU/l points to overt hypothyroidism – both can cause fatigue. High FT4 with suppressed TSH (hyperthyroidism) also leads to exhaustion. Importantly, FT4 in the lower normal range can still be symptomatic for some individuals ('normal labs, sick patients'). Additional tests should include T3, TSH, thyroid antibodies (TPO, Tg), and possibly ultrasound. However, fatigue has many causes: iron deficiency, vitamin D deficiency, sleep disorders, stress, depression. A single FT4 value is too narrow. MyBody-X tests combine blood markers with DNA and microbiome, but evidence for personalized supplement recommendations from genetics alone is weak. For persistent fatigue with abnormal thyroid values, consult an endocrinologist.