Myths vs facts: FT4 and fatigue

FT4 (free thyroxine) is a key thyroid marker, but fatigue alone is not proof of thyroid dysfunction. Fact: Low FT4 can indicate hypothyroidism, which causes fatigue. Myth: A normal FT4 rules out thyroid issues – often TSH, fT3, and antibodies are needed. Also, fatigue has many causes like iron deficiency, poor sleep, stress, or depression. Evidence for the FT4-fatigue link is human-strong, but interpretation requires clinical context. Caveat: Self-testing without medical guidance can lead to misinterpretation. For persistent fatigue, a doctor should evaluate the full thyroid axis and other potential causes.