Thyroid hormone replacement is associated with improvement in renal dysfunction in patients with hypothyroidism: a retrospective observational study.

BACKGROUND: Hypothyroidism is a common endocrine disorder with multisystem involvement and is increasingly recognized as a potentially reversible contributor to renal dysfunction. However, renal impairment related to thyroid hormone deficiency is frequently overlooked or misclassified as chronic kidney disease in clinical practice. METHODS: In this single-center retrospective observational study, 40 hospitalized adults with newly diagnosed hypothyroidism were included. Renal dysfunction was defined by elevated serum creatinine and reduced estimated glomerular filtration rate at admission. All patients received levothyroxine replacement therapy as part of routine care. Biochemical parameters were assessed at three timepoints: admission (T0), normalization of thyroid-stimulating hormone (T1), and normalization of serum creatinine (T2). Serum creatinine was the primary renal outcome, whereas estimated glomerular filtration rate was evaluated as a supportive calculated indicator. Secondary outcomes included thyroid hormones and other biochemical markers. RESULTS: At baseline, mean serum creatinine was 114.88 ± 25.61 μmol/L and estimated glomerular filtration rate was 51.42 ± 16.32 mL/min/1.73 m². Following treatment, serum creatinine decreased significantly to 85.13 ± 21.01 μmol/L at T1 and 79.92 ± 5.64 μmol/L at T2 (both P < 0.01). Estimated glomerular filtration rate improved to 74.48 ± 32.56 and 75.04 ± 14.52 mL/min/1.73 m², respectively. Free thyroid hormone levels increased, while other biochemical parameters showed no consistent changes. Analyses at T1 and T2 were based on responder subgroups that achieved predefined biochemical targets. CONCLUSION: Thyroid hormone replacement was associated with significant short-term improvement in creatinine-based renal indices, suggesting that renal dysfunction in hypothyroidism may be at least partially functional and potentially reversible in some patients. These findings should be interpreted cautiously given the small sample size, retrospective design, responder-based subgroup analyses, absence of a comparison group, and potential residual confounding.