The first case of insulin-dependent diabetes mellitus with prominent spurious hyperglucagonemia due to interference of immunoglobulin G in glucagon radioimmunoassay (OAL-123) system.

A 51-year-old male was admitted to our hospital because of diabetic ketoacidosis. His symptoms were promptly improved with intensive insulin therapy, but his plasma glucagon immunoreactivity measured by the OAL-123 radioimmunoassay (RIA) system showed persistently high values (3,090-3,210 pg/ml). A computed tomographic scan, abdominal angiography and endoscopic examination of his gastrointestinal tract showed no evidence of glucagonoma. After removing the immunoglobulin fraction from the plasma, his immunoreactive plasma glucagon level returned to normal. Moreover, the immunoglobulin G fraction purified from the patient's plasma inhibited the binding of [125I]glucagon to rabbit antiglucagon antiserum, OAL-123. Dot-blot analysis demonstrated that the immunoglobulin G of this patient cross-reacted against OAL-123. Therefore, it was considered that the prominent hyperglucagonemia in this patient was due to the presence of IgG, which interfered with the measurement of plasma-immunoreactive glucagon.