FT3/FT4 ratio in a certain range was identified as an independent protective factor for glycemic variability in patients with type 2 diabetes

Abstract Context: Thyroid hormone (TH) plays a crucial role in regulating glucose metabolism. However, the potential impact of the FT3/FT4 ratio, which reflects peripheral sensitivity to thyroid hormones, on glycemic variability in patients with type 2 diabetes (T2DM), has not been previously reported. Objective: To investigate the correlation between the FT3/FT4 ratio and glycemic variability in individuals with T2DM. Methods: In this retrospective analysis, a total of 468 inpatients with T2DM underwent continuous glucose monitoring (CGM) systems for a period of 6-14 days. Baseline clinical characteristics, laboratory tests, and CGM parameters were documented to investigate the correlation between FT3/FT4 ratio and CGM parameters. Results: The levels of HBA, MG, SD, CV, LAGE, MODD and TAR2Scale were all higher in FT3/FT4Q1 compared with FT3/FT4Q2, FT3/FT4Q3 and FT3/FT4Q4 (all P<0.01). Additionally, TIR was lower in FT3/FT4Q1 compared with the other quartiles (P<0.01). Smooth curve fitting and saturation effect analysis revealed that there are curve-like relationships between the FT3/FT4 ratio and SD, MAGE, MODD and TAR2Scale. The inflection points of the fitted curves were found to be at FT3/FT4=0.279, 0.237, 0.253 and 0.282 respectively (all P<0.05). Prior to the inflection point, the FT3/FT4 ratio was negatively related to SD, MAGE, MODD and TAR2Scale (all P<0.05). Furthermore, The FT3/FT4 ratio exhibits a negative linear correlation with HBA and MG, while demonstrating a positive linear relationship with TIR (all P<0.05). Binary logistic regression demonstrated that the FT3/FT4 ratio was independently related to HBA (P=0.001), MG (P=0.01), TAR2Scale (P=0.003), LAGE (P=0.014) and MAGE (P< 001). Conclusion:The FT3/FT4 ratio plays a crucial role in glycemic control, acting as a protective factor for minimizing glycemic fluctuation in patients with T2DM when it increases within a specific range (FT3/FT4 ≤ 0.282). This suggests that heightened sensitivity to thyroid hormones within a certain range contributes to improved glycemic control and reduced glucose fluctuation.