(HealthDay News) — For patients with type 1 diabetes, long-term weighted mean hemoglobin A1c (HbA1c) is associated with development of severe microvascular complications, according to a study published online December 15 in Diabetes Care.

Maria Nordwall, MD, PhD, from Linköping University in Norrköping, Sweden, and colleagues conduced a longitudinal observation study involving an unselected population of 451 patients diagnosed with type 1 diabetes during 1983–1987, before age 35. The authors measured HbA1c from diagnosis through 20–24 years of follow-up, and calculated long-term weighted mean HbA1c. Complications in relation to HbA1c levels were examined.

The researchers found that increasing long-term mean HbA1c correlated with sharply increased and earlier incidence of proliferative retinopathy and persistent macroalbuminuria. Among patients with long-term weighted mean HbA1c <7.6%, none developed proliferative retinopathy or persistent macroalbuminuria. Among those with long-term mean HbA1c >9.5%, 51% developed proliferative retinopathy and 23% developed persistent macroalbuminuria.

“Keeping HbA1c <7.6% (60mmol/mol) as a treatment target seems to prevent proliferative retinopathy and persistent macroalbuminuria for up to 20 years,” the authors write.

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