Optimal Glycemic and Hemoglobin A1c Thresholds for Diagnosing Diabetes Based on Prevalence of Retinopathy in an Iranian Population

BACKGROUND The use of glycemic thresholds for diabetes diagnosis is controversial. However, no information is available regarding glycemic and glycated hemoglobin (HbA1c) thresholds for detecting diabetic retinopathy (DR) in the Iranian population. OBJECTIVES The main purpose of the current investigation was to examine the association of fasting plasma glucose (FPG) and HbA1c levels with diabetic retinopathy (DR), and to determine the relevant cut-off levels in an Iranian population. PATIENTS AND METHODS This cross-sectional, population-based study was performed during 2012-2013 in Urmia, the capital of West Azerbaijan province, Iran. The subjects were 3,010 Iranians aged 40-81 years. The FPG levels were determined using the glucose oxidase method whereas, the HbA1c values were measured using a standardized assay by high performance liquid chromatography. DR was evaluated by an examination of the fundus photograph of each eye. The photographs were graded according to the international clinical diabetic retinopathy disease severity scale by photograph graders who were masked to the clinical information. RESULTS Of the subjects, 59 had DR. The prevalence of DR increased steeply between the ninth and the tenth deciles for both variables. The ROC curve analysis showed overall glycemic thresholds for DR of 6.5 mmol/L (117 mg/dL) for FPG and 6.2% (44 mmol/mol) for HbA1c. The sensitivities and specificities were 78.0% and 87.1% for FPG and 89.8% and 89.5% for HbA1c, respectively. The areas under the ROC curves indicated that HbA1c was a stronger discriminator of retinopathy: the area under curve was 0.880 for FPG and 0.946 for HbA1c P < 0.001). However, the thresholds for detecting DR for the two measures showed no significant differences after excluding individuals receiving anti-hyperglycemic medication. CONCLUSIONS These findings suggest that the HbA1c and FPG thresholds for detecting diabetes in the Iranian population are lower than the current diagnostic criteria.