Impact of HbA1c followed 32 years from diagnosis of type 1 diabetes on development of severe retinopathy and nephropathy. The VISS-Study

OBJECTIVE To evaluate HbA1c followed from diagnosis, as a predictor of severe microvascular complications i.e., proliferative diabetic retinopathy (PDR) and nephropathy (macroalbuminuria). RESEARCH DESIGN AND METHODS In a population based observational study 447 patients diagnosed with type 1 diabetes before 35 years of age during1983-1987 in South-East Sweden were followed from diagnosis until 2019. Long term weighted mean HbA1c (wHbA1c) was calculated by integrating the area under all HbA1c values. Complications were analyzed in relation to wHbA1c categorized into 5 levels. RESULTS After 32 years 9% had no retinopathy, 64% nonproliferative diabetic retinopathy and 27% PDR, 83% had no microalbuminuria, 9% microalbuminuria and 8% macroalbuminuria. Patients with near normal wHbA1c did not develop PDR or macroalbuminuria. The lowest wHbA1c values associated with development of PDR and nephropathy(macroalbuminuria) were 7.3% (56 mmol/mol) and 8.1% (65 mmol/mol), respectively. The prevalence of PDR and macroalbuminuria increased with increasing wHbA1c being 74% and 44% in the highest category, wHbA1c >9.5% (>80 mmol/mol). In comparison to the follow up done after 20-24 years duration the prevalence of PDR had increased from 14 to 27% and macroalbuminuria from 4 to 8% and both appeared at lower wHbA1c values. CONCLUSIONS WHbA1c followed from diagnosis is a very strong biomarker for PDR and nephropathy, the prevalence of both still increasing 32 years after diagnosis. To avoid PDR and macroalbuminuria in patients with type 1 diabetes HbA1c <7.0% (53 mmol/mol) and as normal as possible should be recommended when achievable without severe hypoglycemia and with good quality of life.