Sociodemographic and biological determinants of insulin initiation in type 2 diabetes: a cohort study using routinely collected primary care data.

Abstract

Timely initiation of insulin is critical to prevent long-term complications associated with poor glycaemic control. A better understanding of the factors influencing insulin initiation is essential to guide person-centred treatment and reduce disparities. To examine factors associated with insulin initiation within 5 years after starting metformin in adults with type 2 diabetes mellitus (T2DM). Cohort study using ELAN primary care data linked to Statistics Netherlands registry data. Adults aged 40-79 years with T2DM who initiated metformin between 2007 and 2023 were included. Fine and Gray competing risk analysis was used to assess time to insulin initiation while accounting for death. Covariates measured within 6 months of metformin initiation included age, sex, smoking status, body mass index (BMI), systolic blood pressure, country of origin, household income, household support, glycosylated haemoglobin (HbA^1c), estimated glomerular filtration rate (eGFR), total cholesterol, and high-density lipoprotein (HDL) cholesterol. Among 24 360 individuals with T2DM on metformin, 2326 (10%) initiated insulin within 5 years. Compared with individuals of Dutch origin, insulin initiation was less likely among people with Surinamese (subdistribution hazard ratio [SHR] 0.62, 95% confidence interval [CI] = 0.45 to 0.79), Turkish (SHR 0.61, 95% CI = 0.30 to 0.91), or other backgrounds other than Dutch (SHR 0.76, 95% CI = 0.61 to 0.90). Higher HbA1c increased the likelihood of insulin initiation (SHR 1.54 per 13 mmol/mol, 95% CI = 1.51 to 1.57). Factors associated with a lower probability of insulin initiation included higher household income (SHR 0.94 per 28% increase, 95% CI = 0.89 to 0.98), overweight or obesity versus having a healthy BMI, older age, higher eGFR, higher HDL, and later calendar year. Besides biological factors, backgrounds other than Dutch and higher household income are linked to a lower probability of initiating insulin therapy.