Free T4 (fT4)
Stomach and gut healthFree T4 is produced by the thyroid gland and converted to active T3 in body tissues.
Why this matters
Free T4 reflects the thyroid gland's production capacity and serves as the primary screening test for thyroid dysfunction. It provides early detection of both hypothyroidism (low fT4) and hyperthyroidism (high fT4) before symptoms become obvious. Because it's unaffected by protein-binding changes, free T4 gives a true picture of thyroid hormone availability, helping distinguish between thyroid disease and conditions that merely affect hormone transport.
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