Dysregulation of the Soluble α-Klotho-FGF23 Axis in Hashimoto's Thyroiditis: A Case-Control Study

Hashimoto's thyroiditis (HT) is the most common autoimmune thyroid disease and is increasingly recognized as a condition associated with chronic low-grade systemic inflammation beyond thyroid hormone dysfunction. The soluble α-Klotho-fibroblast growth factor 23 (FGF23) axis plays a central role in mineral metabolism, inflammation, and aging-related pathways; however, its involvement in HT has not been adequately characterized. This prospective case-control study aims to compare serum soluble α-Klotho and FGF23 levels between adults with Hashimoto's thyroiditis and age- and sex-matched healthy controls, and to investigate their associations with thyroid function parameters, inflammatory markers, and autoimmune burden. In addition, the FGF23/sKlotho ratio will be evaluated as an integrated marker of functional imbalance within the Klotho-FGF23 axis. The study seeks to determine whether Hashimoto's thyroiditis is associated with systemic dysregulation of the Klotho-FGF23 pathway independent of renal function and mineral metabolism.