Normalized Hypothyroidism Linked With Improved Kidney Function

The study covered in this summary was published on Research Square as a preprint and has not yet been peer reviewed.

Key Takeaway

  • In a single-center, retrospective study of 52 patients with overt hypothyroidism — defined as having low levels of free thyroxine (T4) and high levels of thyroid stimulating hormone (TSH) — attainment of normal thyroid function through hormone replacement therapy with levothyroxine was significantly associated with improved kidney function, characterized by decreased proteinuria and serum creatinine and increased estimated glomerular filtration rate (eGFR).

Why This Matters

  • The findings build on prior case reports that reductions in eGFR in patients with hypothyroidism is reversible with replacement therapy and on results from a 2020 prospective, observational study with 43 patients that showed that for patients with severe hypothyroidism, treatment with levothyroxine was linked with increased eGFR and decreased proteinuria.

  • The results suggest that hypothyroidism may be a new, overlooked risk factor for kidney dysfunction and that it may be mostly reversible with levothyroxine treatment and that euthyroidism can be achieved with levothyroxine.

  • The findings also suggest that patients with unexplained elevations in serum creatinine should undergo thyroid hormone testing to assess for possible hypothyroidism.

Study Design

  • A retrospective study included 52 outpatients aged 16 years or older with overt hypothyroidism who were not receiving thyroid medication and who did not have diabetes, hypertension, or any other disorder that could affect urinary protein. The patients were being treated in the Endocrinology Clinic of Kilis State Hospital, in Turkey.

  • After baseline measurements, all patients began a daily regimen of levothyroxine 1.6 μg/kg.

  • Patients underwent follow-up thyroid-function tests at 6-week intervals. When they achieved euthyroidism, they underwent a second round of extensive testing that included 24-hour urinary protein testing, thyroid function testing, and other biochemistry tests.

Key Results

  • The average age of the patients was 41 years; 40 patients (77%) were women.

  • From baseline to euthyroidism, mean values of the following parameters all decreased except for eGFR, which increased (all P ≤ .0004):

    • TSH, from 83 to 1.7 mIU/L (normal value, 0.5 – 4.5 mIU/L)

    • T4, from 0.49 to 1.33 ng/dL (normal value, 0.8 – 2.7 ng/dL)

    • Serum creatinine, from 0.79 to 0.72 mg/dL (both in the normal range)

    • 24-hour urine protein, from 183 to 121 mg/day (normal value, <150 mg/day)

    • eGFR, from 101 to 111 mL/min/1.73 m2 (normal value, ≥90 mL/min/1.73 m2)

  • The following parameters also decreased (all P < .01):