HbA1c better predictor retinopathy than FPG in US population
MedWire News: Study findings show that glycated hemoglobin (HbA1c) is a better predictor of retinopathy prevalence in the general population than fasting plasma glucose (FPG), although high levels of both significantly increase the risk for retinopathy.
The researchers used data from 1066 participants of the 2005–2006 National Health and Nutrition Examination Survey including values for HbA1c, FPG, and 45 degree color digital retinal images. Retinopathy was diagnosed as having a level of 14 or above on the Early Treatment Diabetic Retinopathy Study severity scale.
They found that the mean overall prevalence of retinopathy in this cohort was 11%, compared with a significantly higher prevalence of approximately 36% in patients with known diabetes.
For all participants, retinopathy showed a significant linear increase in prevalence in those with an HbA1c of 5.5% or above or an FPG of 5.8 mmol/l or above, whereas below these cut points prevalence was fairly consistent at around 4-5%. When individuals taking antihyperglycemic medication were excluded, the corresponding values were 5.5% or above or 7.0 mmol/l or above.
Using area under the receiver operator curve analysis (ROC), the team found that HbA1c was a significantly stronger discriminator of retinopathy than FPG, with a score of 0.71 versus 0.65.
“The presence of diabetic retinopathy is arguably the best criterion from which to compare glycemic measures because it is a specific and early clinical complication usually related to diabetes, and it represents a specific and relevant clinical endpoint for judging an alternative test,” write Yiling Cheng (Centers for Disease Control and Prevention, Atlanta, Georgia, USA) and co-authors in the journal Diabetes Care.
For this reason, diabetic retinopathy, or more specifically its associated threshold FPG value of 7.0 mmol/l, has been used in diagnostic criteria for Type 2 diabetes by the American Diabetes Association.
The current study confirms, however, that HbA1c levels could be a superior measure for predicting retinopathy risk to FPG and may be more appropriate for use in diagnosing Type 2 diabetes. As well as a better ROC score, benefits of HbA1c over FPG include the fact that it is less affected by short term lifestyle changes and has less overall variability.
Cheng et al conclude: “While the HbA1c and FPG levels of 5.5% and 5.8 mmol/l provide start points at which retinopathy prevalence increases most precipitously, HbA1c appears to discriminate between the presence and absence of retinopathy at least as well as FPG and offers some advantages over FPG.”
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2009
By Helen Albert