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Functional Hypothyroid

Meaning

Functional Hypothyroid describes a physiological state where an individual exhibits clear clinical symptoms of low thyroid function, such as profound fatigue, inexplicable weight gain, and persistent cold intolerance, despite having serum thyroid-stimulating hormone (TSH) and free thyroxine (FT4) levels within the conventional laboratory reference range. This presentation often reflects an underlying impairment in the peripheral conversion of T4 to the active T3 hormone or a cellular-level resistance to thyroid hormone signaling. It represents a subtle, yet clinically impactful, physiological imbalance often overlooked by standard screening panels.