Association between islet β-cell function and time in range in patients with type 2 diabetes mellitus: a retrospective cross-sectional study.

OBJECTIVE: Impaired islet β-cell function is the core mechanism underlying type 2 diabetes mellitus (T2DM). This study investigated the association between islet β-cell function and time in range (TIR) in patients with T2DM, providing a reference for individualized clinical treatment. METHODS: This retrospective cross-sectional observational l study included 1,160 patients with confirmed T2DM. Participants underwent continuous glucose monitoring (CGM). TIR >70% was defined as achieving the glycemic target. Subjects were divided into three groups based on TIR levels (<70%, 70%-84%, and ≥85%). The β-cell function index HOMA2-β was calculated using the Homeostasis Model Assessment 2 as the core research indicator. RESULTS: The high TIR group had significantly higher HOMA2-β (P < 0.001). Multiple linear regression analysis showed a robust positive correlation between HOMA2-β and TIR after adjusting for covariates (β = 0.402, 95% CI: 0.358-0.447, P < 0.001). Restricted cubic spline (RCS) analysis revealed a significant nonlinear relationship between HOMA2-β and TIR (P for nonlinearity < 0.001). TIR increased with rising HOMA2-β, but the rate of increase gradually slowed. Specifically, when HOMA2-β increased from approximately 10% to 100%, the predicted TIR rose rapidly from about 38% to approximately 96%, representing an increase of 58%. Sensitivity analysis using HOMA2-β calculated from fasting C-peptide instead of fasting insulin yielded consistent conclusions. CONCLUSION: A significant, nonlinear association exists between islet β-cell function HOMA2-β and TIR. TIR levels increase progressively with higher HOMA2-β. Although the cross-sectional design precludes causal inference, these findings provide important reference values for clinical decision-making.