Hemoglobin AIc and red cell oxygen release capacity in relation to early retinal changes in newly discovered overt and chemical diabetics.

The average Hb A1c concentration in consecutive cases of newly discovered nonacidotic diabetics was 11.4% prior to diet and insulin, as compared to 5.5% following prolonged optimal control (p less than 0.001). Hemoglobin A1c was significantly correlated with fasting blood sugar. In a controlled study the average Hb A1c in 30 subjects with chemical diabetes was 5.8% as opposed to 5.3% in controls with normal OGTT (p less than 0.05). Thirty-seven percent of the chemical diabetics had Hb A1c values greater than or equal to 6.5%, while none in the control group showed such high values. Hb A1c in whole blood has increased oxygen affinity. A decrease in red-cell oxygen release was noted in some untreated nonacidotic diabetics, and an adverse effect of insulin on the oxygen release capacity was demonstrated in both newly diagnosed ketoacidotic and nonacidotic diabetics. The importance of this defect in red-cell oxygen-releasing capacity on the function of the microcirculation is discussed. Signs of an early breakdown of the blood-retinal barrier was demonstrated in 20% of the chemical diabetics by fluorescein angiography.