Predictors and Consequences of Delayed Insulin Initiation: A 20-year Retrospective Cohort Study on Diabetes Complications in Southern Thailand

Abstract

Purpose: This study aimed to investigate the prevalence, predictors, and clinical consequences of delayed insulin initiation in patients with type-2 diabetes mellitus in a tertiary care setting. Patients and Methods: A retrospective cohort study was conducted in 973 adults with type-2 diabetes mellitus with initiated insulin therapy between January 1, 2004 and December 31, 2023 at a university hospital in southern Thailand. Delayed insulin initiation was defined as insulin initiation ≥6 months after documented treatment failure (glycated hemoglobin ≥7% on oral agents), reflecting clinical inertia. Logistic regression was used to identify the predictors of delay. Time-to-event analyses and restricted mean survival time were used to compare diabetes-related complications between groups. Results: Delayed insulin initiation occurred in 35% of the patients. Independent predictors included higher body mass index, longer duration of diabetes, biguanide use, and diuretic use, whereas dipeptidyl peptidase-4 inhibitor use was associated with timely initiation. Although no significant differences were observed in overall macrovascular or microvascular complication rates, delayed initiation was significantly associated with increased amputation risk (hazard ratio: 2.33; 95% confidence interval: 1.07–5.07) and earlier onset of microvascular complications within the 10–15-year window (restricted mean survival time difference: −0.56 years, p=0.043). Conclusion: Delayed insulin initiation is common and linked to identifiable clinical characteristics and adverse outcomes, including increased risk of amputation and earlier microvascular complications. Prioritizing timely insulin initiation is essential to reduce long-term complications and preserve limb health, particularly in high-risk individuals.