To investigate the effect of subclinical hypothyroidism (SCH) on the progression of early diabetic kidney disease (DKD) in type 2 diabetic patients.

A retrospective study was performed in 260 patients with early type 2 diabetic kidney disease [estimated glomerular filtration rate (eGFR) greater than 60 ml·min^-1· (1.73 m²) ^-1], who were repeatedly hospitalized in Tianjin Medical University Metabolic Diseases Hospital for more than 3 times from January 2008 to August 2018, including 198 patients with normal thyroid function and 62 patients with subclinical hypothyroidism. The first hospitalization was defined as the starting point, the last hospitalization was defined as the study endpoint. According to the levels of thyroid-stimulating hormone (TSH), free triiodothyronine and free thyroxine, the patients were divided into two groups: type 2 diabetes with normal thyroid function group (DM+EUT) and type 2 diabetes with subclinical hypothyroidism group (DM+SCH). The clinical data and renal function indicators of each hospitalization were collected. The average annual decreasing rate of eGFR (eGFR/Y), the average annual increasing rate of 24-hour total urine protein (24 h-TP/Y) and 24-hour urine microprotein (24 h-UMA/Y) were compared between these two groups. The influence factors of eGFR/Y were analyzed by Pearson or Spearman correlation and multiple linear regression.

There were no significant differences in baseline blood urea nitrogen, serum creatinine, uric acid between these two groups (t=-0.692, -1.432, -0.987, respectively, P>0.05). There were no statistical differences in the 24 h-TP and 24 h-UMA between these two groups (Z=-1.536, -1.412, P>0.05). The baseline eGFR in the DM+SCH group was lower than that in the DM+EUT group [(96.5±41.9) vs (99.4±42.2) ml·min^-1· (1.73 m²) ^-1, t=1.695, P=0.095], but the difference had no statistical significant. The eGFR/Y in the DM+SCH group was significantly higher than that in the DM+EUT group [6.02 (2.31, 8.92) vs 4.32 (1.35, 6.01) ml·min^-1· (1.73 m²) ^-1, Z=-2.241, P=0.02]. There was no significant difference in 24 h-TP/Y and 24 h-UMA/Y between these two groups (P>0.05). After adjustment for potential confounding factors (24 h-TP, systolic blood pressure and baseline eGFR) by multiple linear regression analysis, TSH remained to be associated with eGFR/Y significantly (t=2.149, P=0.036).

TSH is an independent risk factor for the average annual decreasing rate of eGFR. SCH can accelerate the progression of early DKD in type 2 diabetic patients.

Diabetes mellitus, type 2; Glomerular filtration rate; Thyrotropin; Subclinical hypothyroidism