Residual β-cell function is associated with longer time in range in individuals with type 1 diabetes

Objective. Little is known about the influence of residual islet function on glycemic control in type 1 diabetes (T1D). Therefore, we investigated the associations between residual β-cell function and metrics of continuous glucose monitoring (CGM) in individuals with T1D.

Research design and methods. In this cross-sectional cohort, comprised of 489 individuals, 64% was female, age was 41.0±14.0 years, T1D duration was 15.0 [IQR 6.0-29.0] years. Individuals had a time in range (TIR) of 66% [IQR 52-80] and UCPCR of 0.01 [IQR 0.00-0.41] nmol/mmol. To assess β-cell function, we measured urinary C-peptide/creatinine ratios (UCPCR, detectable >0.01nmol/mmol) and to assess α-cell function fasting plasma glucagon/glucose ratios were measured. CGM was used to record TIR (3.9-10 mmol/L), time below range (TBR) (<3.9 mmol/L), time above range (TAR) (>10 mmol/L) and coefficient of variance (CV). For CGM, 74.7% used Freestyle Libre-2, 13.8% Metronic-Guardian and 11.5% DexcomG6 as device.

Results. 49.4% of T1D had detectable UCPCR. A higher UCPCR correlated with higher TIR (r=0.330, p <0.05), lower TBR (r=-0.237, p <0.05), lower TAR (r=-0.302, p <0.05), and lower CV (r=-0.356, p <0.05), respectively. A higher UCPCR correlated negatively with HbA1c levels (r =-0.183, p <0.05) and total daily insulin dose (r=-0.183, p <0.05). Glucagon/glucose ratios correlated with longer TIR (r=0.234, p <0.05).

Conclusions. Significantly longer TIR, shorter TBR and TAR and lower CV were observed in individuals with greater UCPCR-assessed β-cell function. Therefore, better CGM-derived metrics in individuals with preserved β-cell function may be a contributor to a lower risk of developing long-term complications.