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Glycemic Levels Predict Risk of Retinopathy

Posted: Sunday, February 27, 2011

Both short- and long-term measures of blood glucose can be used to predict the risk of retinopathy.

In a cohort study, the risk of the condition shot up markedly when fasting plasma glucose and glycated hemoglobin (HbA1c) reached levels that are used to indicate diabetes risk, according to Beverley Balkau, PhD, of the Institut National de la Santé et de la Recherche Médicale in Villejuif, France, and colleagues.

The finding allows physicians to set threshold values that define patients at risk of the eye condition. Balkau and colleagues studied more than 700 men and women taking part in the DESIR study, which enrolled volunteers ages 30 to 65 in western France from 1994 to 1996.

The goal was to study the frequency of retinopathy in individuals 10 years after measuring baseline levels of fasting plasma glucose and HbA1c and to evaluate positive predictive values for retinopathy at various levels of the glycemic variables.

After a baseline health exam, all participants were asked to return for subsequent examinations three, six, and nine years later. Those who were diagnosed with diabetes or who had had a fasting glucose level of at least 126 mg/dL at any point during the study were asked to undergo testing for retinopathy using a nonmydriatic digital retinal camera.

For comparison, two groups of matched participants also had the retinal exam -- those who had had an impaired fasting glucose level (from 110 through 125 mg/dL) at any time during the study and those whose glucose levels had always been below 110 mg/dL.

All told, the researchers found 44 participants with retinopathy, including 19 of 237 in the diabetes group, another 19 of 246 with impaired glucose levels, and six of 249 in the normal glucose group.

Those with retinopathy had higher baseline fasting glucose and HbA1c levels on average -- 106 versus 130 mg/dL and 6.0% versus 6.4%, respectively (P<0.001). A higher percentage were treated for hypertension -- 36.4% of those with retinopathy compared with 19.6% (P=0.008), and they had a trend toward higher systolic blood pressure.
Analysis also showed that:

* Fasting plasma glucose levels of 108 and 116 mg/dL had positive predictive values of 8.4% and 14.0%, respectively, for retinopathy.
* HbA1clevels of 6.0% and 6.5% had positive predictive values of 6.0% and 14.8%, respectively.

Because of the sharp increase, they argued, the lower levels of each marker should be used as thresholds to identify those at risk of retinopathy 10 years down the road.

Balkau and colleagues noted that the study's strengths included a large sample size and long follow-up. However, they cautioned that the study participants were self-selected individuals who volunteered for the study after a free health checkup and the sample size of those with retinopathy was small, allowing evaluation only of risk factors strongly associated.

Practice Pearls

* Explain that higher fasting plasma glucose and HbA1c increased the risk of retinopathy when follow-up digital retina imaging was performed 10 years later.

* Note that the investigators recommend using thresholds of 108 mg/dL for fasting plasma glucose and 6.0% for HbA1c to predict those at higher risk for later developing retinopathy.

Source: http://www.diabetesincontrol.com/index.php?option=com_content&view=article&id=10552&catid=53&Itemid=8, Archives of Ophthalmology, 2011: 129(2): 188-195; Massin M, et al.