Fasting C-peptide, a biomarker for hypoglycaemia risk in insulin-naïve people with type 2 diabetes initiating basal insulin glargine 100 U/mL.

AIM: To examine the relationship between baseline fasting C-peptide (FCP) and outcomes in insulin-naïve people with type 2 diabetes initiating basal insulin glargine 100 U/mL (Gla-100).
MATERIALS AND METHODS: Post hoc pooled analysis of nine randomized, treat-to-target trials in patients with type 2 diabetes inadequately controlled on oral antihyperglycaemic drugs initiating once-daily Gla-100. Participants (n = 2165) were stratified at baseline according to FCP (≤0.40, >0.40-1.20, >1.20-2.00, >2.00 nmol/L). Glycaemic control, body weight, insulin dose and hypoglycaemia were determined at 24 weeks.
RESULTS: At baseline low FCP levels were associated with longer known diabetes duration, lower body mass index and higher fasting plasma glucose (FPG). Following Gla-100 introduction, the mean HbA1c reduction at week 24 was similar in all four FCP groups, albeit fewer people in the lowest FCP group achieved HbA1c <7.0% versus FCP groups >0.40 nmol/L. By contrast, FPG reduction and proportion reaching FPG ≤5.6 mmol/L were greatest in the lowest FCP group, diminishing at higher FCP levels. Gla-100 dose at week 24 was lowest in the ≤0.40 nmol/L FCP group and highest in the >1.20 nmol/L FCP group. Incidence and event rate of overall, nocturnal and severe hypoglycaemia were higher at week 24 in groups with lower FCP levels. In multivariable regression analysis baseline FCP, concomitant sulphonylurea use and endpoint HbA1c were strong predictors of hypoglycaemia.
CONCLUSIONS: FCP levels identified patients with type 2 diabetes experiencing different responses to basal insulin Gla-100. A low FCP identifies a markedly insulin-deficient, insulin-sensitive subgroup/phenotype with an enhanced risk of hypoglycaemia, which requires a low initial basal insulin dose, cautious titration and earlier addition of prandial glucose-lowering therapy.