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.
Key Findings
Results
Serum creatinine decreased significantly following levothyroxine replacement therapy at both post-treatment timepoints.
Baseline (T0) mean serum creatinine was 114.88 ± 25.61 µmol/L
Serum creatinine decreased to 85.13 ± 21.01 µmol/L at T1 (TSH normalization) and 79.92 ± 5.64 µmol/L at T2 (creatinine normalization)
Both reductions were statistically significant (P < 0.01)
Analyses at T1 and T2 were based on responder subgroups that achieved predefined biochemical targets, not the full cohort of 40 patients
Results
Estimated glomerular filtration rate (eGFR) improved following levothyroxine treatment.
Baseline eGFR was 51.42 ± 16.32 mL/min/1.73 m², consistent with moderately reduced kidney function
eGFR improved to 74.48 ± 32.56 mL/min/1.73 m² at T1 and 75.04 ± 14.52 mL/min/1.73 m² at T2
eGFR was evaluated as a supportive calculated indicator rather than a primary outcome
The improvement represents a mean increase of approximately 23 mL/min/1.73 m² from baseline to T1
Results
Free thyroid hormone levels increased following levothyroxine replacement, while other biochemical parameters showed no consistent changes.
Free thyroid hormone levels increased following treatment as expected with levothyroxine replacement
Other biochemical markers assessed did not show consistent changes across the timepoints studied
Biochemical parameters were assessed at three timepoints: admission (T0), normalization of TSH (T1), and normalization of serum creatinine (T2)
Methods
The study enrolled 40 hospitalized adults with newly diagnosed hypothyroidism, all of whom had renal dysfunction at baseline.
This was a single-center retrospective observational study
Renal dysfunction was defined by elevated serum creatinine and reduced eGFR at admission
All patients received levothyroxine replacement therapy as part of routine clinical care
No comparison group without levothyroxine treatment was included
Background
Renal impairment related to thyroid hormone deficiency is frequently overlooked or misclassified as chronic kidney disease in clinical practice.
Hypothyroidism is described as 'a potentially reversible contributor to renal dysfunction'
The authors note this misclassification as a motivation for the study
The findings suggest that some cases of apparent CKD in hypothyroid patients may represent functional, reversible impairment rather than structural kidney disease
Discussion
The authors identified several important limitations that require cautious interpretation of the findings.
Small sample size of 40 patients
Retrospective design without randomization or blinding
Responder-based subgroup analyses at T1 and T2 (not all 40 patients achieved the predefined biochemical targets)
Absence of a comparison group
Potential residual confounding not fully accounted for
What This Means
This research suggests that kidney problems seen in patients with hypothyroidism (an underactive thyroid) may not always be permanent. In a study of 40 hospitalized patients newly diagnosed with hypothyroidism, all of whom had reduced kidney function at the time of admission, treatment with levothyroxine (a standard thyroid hormone replacement medication) was associated with meaningful improvements in kidney function markers. Specifically, a key measure of kidney waste filtration (serum creatinine) dropped substantially after thyroid hormone levels were restored to normal, and estimated kidney filtration rates improved from levels indicating moderate impairment to levels closer to normal range.
This matters because kidney disease and thyroid disease can look similar in blood tests, and clinicians may sometimes label thyroid-related kidney problems as chronic kidney disease — a permanent condition — when they might actually be reversible. This research suggests that in some hypothyroid patients, what appears to be kidney disease may actually be a functional consequence of low thyroid hormone that improves once the thyroid problem is treated. However, the study has significant limitations: it included only 40 patients at a single hospital, had no comparison group of untreated patients, used a retrospective design, and the follow-up analyses were performed only on the subset of patients who responded to treatment. These factors mean the findings cannot be used to draw firm conclusions and need to be confirmed in larger, more rigorously designed studies before changing clinical practice.
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Zhao T, Zhang N, Tian Y, Yang Z. (2026). Thyroid hormone replacement is associated with improvement in renal dysfunction in patients with hypothyroidism: a retrospective observational study.. Frontiers in endocrinology. https://doi.org/10.3389/fendo.2026.1840954