Glycated albumin (GA) and the GA/HbA1c ratio are higher in diabetic patients positive for insulin antibodies with high binding capacity and low affinity

Patients with diabetes mellitus having insulin antibodies (InsAb) with properties of high binding capacity and low affinity, which are observed in insulin autoimmune syndrome (IAS), are known to have greater plasma glucose fluctuations. Glycated albumin (GA) and the GA/HbA1c ratio have been demonstrated to reflect plasma glucose fluctuations. Hence, we hypothesized that GA or the GA/HbA1c ratio in diabetic patients having InsAb with properties of high binding capacity and low affinity may be higher than those in InsAb-negative diabetic patients, and we verified this hypothesis. Subjects were 12 diabetic patients who had InsAb noted while being treated with insulin and were subjected to Scatchard analysis and whose InsAb had properties similar to those of patients with IAS (affinity constant K1 < 0.24 × 1/10 –8 M, number of binding sites R1 ≥ 11.5 × 10 –8 M) [four cases of type 1 diabetes (T1D) and eight cases of type 2 diabetes (T2D)]. The control group consisted of T1D and T2D cases matched to the T1D and T2D cases, respectively, according to sex, age, BMI, and HbA1c. GA and the GA/HbA1c ratio were compared between both groups. GA and the GA/HbA1c ratio in InsAb-positive patients was significantly higher than that in the control group for both T1D and T2D patients. Diabetic patients having InsAb with properties of high binding capacity and low affinity had higher GA and the GA/HbA1c ratio than those of InsAb-negative patients. Greater plasma glucose fluctuations were suggested in InsAb-positive diabetic patients.