Association between free triiodothyronine, resting metabolic rate, systemic immune-inflammation index levels and diabetic retinopathy in type 2 diabetic patients with euthyroidism

Introduction Thyroid hormones (TH) play important role in retinal development and maintaining retinal functional hemostasis. Resting metabolic rate (RMR) provides an estimate of the minimum amount of energy expenditure and has a bearing on insulin resistance. Systemic immune-inflammation index (SII) is a new inflammatory biomarker associated with diabetic complications. Inflammation and energy metabolism imbalance are closely related to the pathogenesis of diabetes retinopathy (DR). However, few studies have investigated the relationship between TH, RMR, SII and DR in type 2 diabetic patients (T2DM) with euthyroidism. This study aims to investigate the association of TH, RMR and SII with DR in Chinese T2DM patients with euthyroidism. Methods This cross-sectional study was performed in 819 T2DM patients with euthyroidism. Patients were divided into NDR group (n=609) and DR group (n=210). Baseline data and biochemical parameters of patients were collected. Spearman’s correlation analysis, receiver operating characteristic (ROC) curve analysis and logistic regression analysis were performed to examine the association between TH, RMR, SII and DR. Results Compared with NDR patients, the FT3 levels were significantly lower in DR patients, no differences were found in FT4 and TSH levels between the two groups. Furthermore, the SII levels were significantly higher while RMR were lower in DR patients. In multivariate analysis, FT3 and RMR were inversely while SII were positively correlated with the occurrence of DR in T2DM patients with euthyroidism. After adjusting for age and sex, fourth quartile of FT3 showed significantly decreased OR of 0.615 while SII showed increased OR of 1.660 for DR with respect to its first quartile value. In the fully adjusted models, fourth quartile of RMR showed significantly decreased OR of 0.291 for DR with respect to its first quartile value. Conclusion In euthyroidism patients with T2DM, decreased FT3, RMR and increased SII were correlated with the presence of DR.