New diabetes diagnostic threshold of hemoglobin A1cand the 3-year incidence of retinopathy

Abstract

The new diagnostic threshold of hemoglobin A1c was made based on evidence from cross-sectional studies, and no longitudinal study supports its validity. To examine whether hemoglobin A1c of 6.5% or higher defines a threshold for elevated risk of incident retinopathy, we analyzed longitudinal data of 19,897 Japanese adults who underwent a health checkup in 2006 and were followed up 3 years later. We used logistic regression models and restricted cubic spline models to examine the relationship between baseline hemoglobin A1c levels and the prevalence and the 3-year incidence of retinopathy. The restricted cubic spline model indicated a possible threshold for the risk of incident retinopathy at hemoglobin A1c levels of 6.0-7.0%. Logistic regression analysis found that individuals with hemoglobin A1c levels of 6.5-6.9% were at significantly higher risk of developing retinopathy at 3 years compared with those with hemoglobin A 1c levels of 5.0-5.4% (adjusted odds ratio, 2.35 [95% CI 1.08-5.11]). Those with hemoglobin A1c levels between 5.5 and 6.4% exhibited no evidence of elevated risks. We did not observe a threshold in the analysis of prevalent retinopathy. Our longitudinal results support the validity of the new hemoglobin A1c threshold of 6.5% or higher for diagnosing diabetes. © 2012 by the American Diabetes Association.