Long-term glycaemic control and complications in Type 1 diabetes

Abstract: The impact of long-term glycaemic control, assessed by HbA1c measurements for five years or more, on diabetic retinopathy, nephropathy, and impaired vibration perception threshold was investigated in adult patients with Type 1 diabetes mellitus. Type 1 diabetes was defined as onset of diabetes before the age of 31, with insulin therapy introduced within 6 months from onset, and with no other known cause of insulin deficiency. A comparison of glycated haemoglobin values, as assessed in different long-term studies of the relationship between glycaemic control and diabetic complications was also made.High long-term mean HbA1c was shown to be strongly associated to development of proliferative retinopathy and nephropathy, and the severity of background retinopathy and impairment of vibration perception threshold in patients with 5-25 yr duration of diabetes. Patients who developed proliferative retinopathy had a long-tenn mean HbA1, of 8.9% (95% Cl 8.1-9.6%, nonnal range 3.5-5.5% HbA1,), and patients who developed nephropathy had a long-term mean HbA1c of &.8% (95% Cl 7 .8-9.9%) prior to the diagnosis of these complications. Patients with HbA1c >8% also had a relative risk of 6.3 (95% Cl 2.9l00% above the normal range, and no patient with HbA1c below 6.5% had> 100% elevated VPT.Low long-term HbA1c was a beneficial factor for avoidance of retinopathy, but was of less importance to prevent microalbuminuria after more than 20 yr of diabetes. No patient with long-term mean HbA1c above 7.3% avoided retinopathy for such a long period, while patients with normoalbuminuria had HbA1c values in the range 4.6-9.9%.Men tended to have more severe lesions than women, without a corresponding gender difference in glycaemic control. Elevated blood pressure was found to be associated with nephropathy, retinopathy, and impaired vibration perception threshold.In the comparison of glycated haemoglobin values from different long-term studies of glycaemic control and complications of diabetes, the differences between the highest and lowest results of the same sample were, on average 2% HbA1c. This difference is of the same magnitude as the reported difference in glycaemic control between intensified and regular treatment in interventional studies.In conclusion, long-term mean HbA,c is a strong predictor of diabetic complications in the individual patient. Standardisation of HbA1c methods, regular monitoring of HbA1c, and intervention aiming at avoidance of poor glycaemic control is therefore essential.

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