OBJECTIVEHbA 1c is strongly related to the development of diabetes complications, but it is still controversial which HbA 1c level to strive for in the treatment of type 1 diabetes. The aim of the current study was to evaluate HbA 1c , followed from diagnosis, as a predictor of severe microvascular complications and to formulate HbA 1c target levels for treatment. RESEARCH DESIGN AND METHODSA longitudinal observation study followed an unselected population of 451 patients diagnosed with type 1 diabetes during 1983-1987 before the age of 35 years in a region of Southeast Sweden. Retinopathy was evaluated by fundus photography and nephropathy data collected from medical records. HbA 1c was measured starting from diagnosis and during the whole follow-up period of 20-24 years. Long-term weighted mean HbA 1c was then calculated. Complications were analyzed in relation to HbA 1c levels. RESULTSThe incidence of proliferative retinopathy and persistent macroalbuminuria increased sharply and occurred earlier with increasing long-term mean HbA 1c . None of the 451 patients developed proliferative retinopathy or persistent macroalbuminuria below long-term weighted mean HbA 1c 7.6% (60 mmol/mol); 51% of the patients with long-term mean HbA 1c above 9.5% (80 mmol/mol) developed proliferative retinopathy and 23% persistent macroalbuminuria. CONCLUSIONSLong-term weighted mean HbA 1c , measured from diagnosis, is closely associated with the development of severe complications in type 1 diabetes. Keeping HbA 1c below 7.6% (60 mmol/mol) as a treatment target seems to prevent proliferative retinopathy and persistent macroalbuminuria for up to 20 years.

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