Type 1 diabetes is a complex disease, and development of multiple complications over time can be analyzed only with advanced statistical methods. This study describes the development of microvascular complications and explores the effect of complication burden and important concurrent risk factors by applying a multistate model.

We used a clinical cohort at the Steno Diabetes Center Copenhagen to study the development of diabetic kidney disease, retinopathy, and neuropathy. We extracted information from electronic patient records and estimated incidence rates of complications by concurrent complication burden. We explored the extent to which concurrent complications modify the effect of selected risk factors on the development of microvascular complications.

We included 3,586 individuals. Incidence rate ratios in individuals with two previous complications were 3.2 (95% CI 2.3–4.5) for diabetic kidney disease, 2.1 (1.5–3.1) for retinopathy, and 1.7 (1.2–2.4) for neuropathy compared with individuals without complications. The models included diabetes duration; calendar time and age as timescales; and sex, HbA_1c, lipid-lowering and antihypertensive treatment, systolic blood pressure, BMI, estimated glomerular filtration rate (eGFR), cardiovascular disease (CVD), LDL cholesterol, insulin dose (units/kg/day), and smoking status as covariates. Effects of HbA_1c, diabetes duration, systolic blood pressure, BMI, eGFR, and LDL cholesterol where not modified by concurrent complication burden, whereas the effect of sex and CVD were.

The risk of microvascular complications highly depends on the concurrent complication burden and risk factor profile in individuals with type 1 diabetes. The results emphasize attention to risk factors, regardless of existing number of complications, to prevent development of further microvascular complications.