Predictors of HbA1c over 4 years in people with type 2 diabetes starting insulin therapies: The CREDIT study.

AIMS To identify factors associated with glucose control, as measured by HbA1c over 4 years, in people with type 2 diabetes starting insulin therapy. METHODS CREDIT, an observational cohort study, collected data semi-annually over 4 years, on people with type 2 diabetes starting any insulin, in 311 centres in 12 countries; 2803 people had data on HbA1c during follow-up. Multivariable backward regression analysis selected characteristics associated with glycaemic control from a limited number of candidate variables. RESULTS Before starting insulin therapy, HbA1c was 9.3% (78 mmol/mol) and decreased to 7.6% (60 mmol/mol) after 1 year, and changed little after that. Insulin dose increased from 0.21 U/kg to 0.36 U/kg at 1 year, and then by 0.10 U/kg over the next 3 years. Body weight increased by 2.0 kg in the first year and increased little thereafter. Poorer glycaemic control over the 4 years was mainly determined by the HbA1c before starting therapy, after accounting for the other statistically significant associated variables in multivariable analysis: higher BMI, younger age, longer diabetes duration, more glucose-lowering drugs, using basal insulin alone, higher insulin dose and female sex. At 4 years, a higher current insulin dose was the characteristic most strongly associated with a higher concurrent HbA1c. CONCLUSIONS HbA1c at the start of insulin therapy was the characteristic most predictive of later HbA1c, after accounting for other variables associated with HbA1c. This may provide some justification for earlier insulin introduction to improve glucose control to target.