Is TSH useful for fatigue?

TSH (thyroid-stimulating hormone) is a well-established screening test for thyroid dysfunction, which can cause fatigue. However, isolated TSH is insufficient to explain fatigue because many other factors (iron deficiency, sleep disorders, stress, inflammation) contribute. The evidence for TSH as a fatigue marker is moderate: strong for overt hypo- or hyperthyroidism, but often non-specific for subclinical changes. Consumer lab tests (e.g., MyBody-X) offer TSH, but interpretation requires a physician. Caveat: Normal TSH does not fully rule out thyroid issues (e.g., central hypothyroidism). Evidence: human-moderate (clinical guidelines).