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Jing Xie, Suganya Selvarajah, Ryo Kawasaki, Theona Elena Nicolaou, Sutha Sanmugasundram, Jie Jin Wang, Tien Yin Wong, Ecosse Lamoureux; How much does glycated hemoglobin A1c explain the risk of diabetic retinopathy in persons with type 2 diabetes? The Diabetes Management Project (DMP). Invest. Ophthalmol. Vis. Sci. 2012;53(14):5742.
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Although hyperglycemia is a major risk factor for diabetic retinopathy (DR) in persons with type 1 diabetes, the relationship of hyperglycemia and DR in persons with type 2 diabetes is less clear. This study aimed to determine the contribution of glycated hemoglobin A1c (HbA1c) in explaining the risk of DR in persons with type 2 diabetes.
Patients were recruited from eye clinics in Melbourne, Australia. Each participant underwent a comprehensive eye examination and completed standardized interview-administered questionnaires. Blood samples were assessed for HbA1c; fasting blood glucose; and serum lipids. Dilated fundus photographs (two-field) were obtained and graded for the severity of DR. Commonality analysis was used to partition the regression effect of HbA1c into unique and common effects. Unique effect identifies how much variance is unique to HbA1c, and common effect identifies the joint effect of HbA1c and other risk factors.
A total of 497 patients with type 2 diabetes aged between 26 and 90 years (median 65.0 years) were included in this analysis. Among these, 60% had any DR. Age, gender, HbA1c, duration of diabetes, and insulin use were significantly associated with any DR, accounting for 45% of the total variance. The unique and common effects of HbA1c on DR were 2.1% and 6.4%, respectively. The most importance risk factor for any DR was duration of diabetes, with a 7.9% and 8.7% of unique and common variances, respectively. Combining HbA1c, duration of diabetes and insulin use explained a total of 38.0% variance (13% of unique variance and 25.0% of common variance). Subgroup analysis showed the effect of HbA1c was higher in patients with PDR (unique variance: 3.0%; common variance: 9.1%).
Although clinical trials and epidemiological studies suggest it is important to target hyperglycemia to prevent diabetic retinopathy, our study suggests that HbA1c alone accounts for only a small proportion of the risk of DR. Targeting glycemic control alone is not sufficient to prevent DR in type 2 diabetes and a multifactorial risk management is needed.
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