Autoimmune Hypoglycemia in a Type 2 Diabetic Patient With Anti-Insulin and Insulin Receptor Antibodies

Response to Kim et al.

Kim et al. (1) recently reported autoimmune hypoglycemia in a type 2 diabetic patient with anti-insulin and insulin receptor antibodies. The patient was a 72-year-old woman with suitable clinic and laboratory data for autoimmune hypoglycemia. Her plasma glucose was 40 mg/dl, insulin 103.7 μU/ml, and C-peptide 4.1 ng/ml. The authors state, “Patients with this condition have low circulation insulin, C-peptide levels, and refractory hypoglycemia.” We believe that this sentence is discordant with the rest of the letter and patients’ given data.

Hypoglycemia owing to insulin antibodies is rare but should be considered in any patient with hypoglycemia in the setting of nonsuppressed insulin levels, i.e., insulin levels that are markedly elevated, usually >100 μU/ml, as in the given patient (2). Free insulin levels may be normal or high, and C-peptide levels are not suppressed (3).

In hypoglycemia due to insulin receptor antibodies, insulin levels are usually higher than appropriate for the glucose concentration. This finding raises the possibility of a pancreatic tumor (4); however, C-peptide and proinsulin levels are usually appropriately low during hypoglycemia, which helps distinguish the condition from insulinoma.