Contributions of fasting and postprandial glucose to hemoglobin A1c.

OBJECTIVE To define the respective contributions of fasting and postprandial plasma glucose to hemoglobin A1c (HbA1c) in patients with non-insulin-treated type 2 diabetes. METHODS Previous studies of diurnal glycemic profiles are reviewed, and glucose values for predicting successful treatment of diabetes are suggested. RESULTS By analyzing the results from prior studies of diurnal glycemic profiles, we found that the relative contribution of postprandial plasma glucose was high (70%) in patients with fairly good control of diabetes (HbA1c <7.3%) and decreased progressively (30%) with worsening diabetes (HbA1c >10.2%). In contrast, the contribution of fasting plasma glucose showed a gradual increase with increasing levels of HbA1c. By using the same model (the diurnal glycemic profile), we established that post-meal glycemia was a better predictor of good or satisfactory control of diabetes (HbA1c <7%) than was fasting glucose. The best cutoff values that ensured the optimal balance between high sensitivity and specificity were approximately 200 mg/dL at 11 AM and 160 mg/dL at 2 PM. The cut-point values for predicting treatment success (specificity (3) 90%) were 162 mg/dL at 11 AM and 126 mg/dL at 2 PM. CONCLUSION Postprandial plasma glucose is the predominant contributor in patients with satisfactory to good control of diabetes, whereas the contribution of fasting plasma glucose increases with worsening diabetes. Postmeal thresholds for predicting good or satisfactory control of diabetes are dependent on the timing of the meals.