Thyroid hormones and diabetic nephropathy: An essential relationship to recognize.

AIMS: Although abnormal thyroid hormone metabolism is common in patients with type 2 diabetes mellitus (T2DM) and diabetic nephropathy (DN), the relationship between thyroid hormones and DN is unclear and has been ignored during clinical practice. This study aimed to investigate the relationship between thyroid hormones and clinicopathologic changes in biopsy-proven DN patients.

METHODS: Clinical and pathological data for 146 biopsy-proven DN patients were collected. The patients were divided into four groups: euthyroid group, high-thyroid stimulating hormone (TSH) group (SCH), low-free triiodothyronine (FT3) group (with normal levels of TSH and FT4), and high-TSH + low-FT3 group (with normal levels of FT4). The clinicopathologic features among the four groups were investigated. We evaluated the risks of abnormal thyroid hormone levels on DN by logistic regression with multivariable adjustments for other risk factors. We also performed quarterback and eight-point analyses of TSH and FT3 levels to determine their influences on DN.

RESULTS: The overt proteinuria (>5 g/24 h) (P = 0.008) and severity of glomerular lesions (P = 0.011) differed between euthyroid group and high-TSH group significantly. Moreover, the levels of estimated glomerular filtration rate (P =0.019), serum creatinine (P =0.014), and severity of glomerular lesions (P =0.003) differed between the euthyroid group and low-FT3 group significantly. There were also significant differences between high-TSH, low-FT3 and high-TSH + low-FT3 patients, respectively. Respective correlations between high-TSH, low-FT3 and renal clinicopathologic changes were found to be significant according to logistic regression analyses. Quarterback and eight-point analyses indicated that patients with TSH levels of 4.54-5.67 mU/L had the most severe renal clinicopathologic changes, and the severity of renal changes decreased with increased FT3 levels.

CONCLUSIONS: Diabetic nephropathy patients with high-TSH and/or low-FT3 had more severe proteinuria, renal insufficiency, and glomerular lesions, suggesting that regulating thyroid hormones might have a renoprotective effect.