HbA1c variability Predicts Nephropathy, Retinopathy in Type 1 Diabetes

Specifically, development of nephropathy and retinopathy can be better predicted based on long-term fluctuations in HbA1c variability, according to researchers from the Hull Royal Infirmary, University of Hull and Hull York Medical School in the United Kingdom.

The researchers analyzed data from the DCCT — a nine-year follow-up study that compared the effect of intensive vs. conventional blood glucose control on the development of microvascular complications in 1,441 patients with type 1 diabetes.

Variability in HbA1c added to the mean value in prediction of risk or progression to nephropathy (HR=1.80; 95% CI, 1.37-2.42) and retinopathy (HR=2.26; 95% CI, 1.63-3.14), according to multivariate Cox regression.

Patients assigned to conventional blood glucose control experienced greater HbA1c variability than patients assigned to intensive blood glucose control (SD, 0.86 vs. 0.59). According to the researchers, the pronounced effect in the conventionally treated group was “presumably because the event rate, range of variability and spread of variability at any given mean HbA1c was much larger than those for patients in the intensively treated group (r=0.71 vs. r=0.32).”
“This study has shown that longer-term fluctuations in glycemia seem to independently relate to the development of retinopathy and nephropathy in type 1 diabetes. Thus, sole measurement of mean glucose or mean HbA1c may not be the best predictor of complication risk,” the researchers wrote.

These findings are in contrast to a previously published DCCT analysis that concluded HbA1c variability did not strongly affect risk for diabetes complications.  You might also assume that  fluctuations in HbA1c undoubtedly represents periods of poor glycemic control which would increase the risk for retinopathy.
Diabetes Care. 2008;31:2198-2202.