Insulin autoimmune syndrome without hypoglycemia: A different perspective of method interference.

Insulin autoimmune syndrome (IAS) is a serious autoimmune disorder that may cause spontaneous hypoglycemia. IAS is characterized by hyperinsulinemia, normal C-peptide levels and positive anti-insulin antibody. The diagnosis is confirmed by demonstrating the presence of macroinsulin complex by polyethylene glycol (PEG) precipitation or gel filtration chromatography. Although some macrohormones like macroprolactin and some macroenzymes such as macroamylase are seen commonly, macroinsulinemia is a rare condition. In this report, we presented an IAS case from laboratory perspective by using three different immunoassays with different performances in eliminating macroinsulin interference. Besides presenting a case with IAS without hypoglycemia we evaluated the contribution of different immunoassays to the diagnosis of this syndrome. Immunoassays have different features, considering the analysis of macroinsulin or bioavailable insulin. In this case, the superiority or handicap of these immunoassays will be discussed in terms of analysis of total or free insulin.