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 ke toacidosis. 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 a nd endoscopic examination of his gastrointestinal tract showed no evid ence of glucagonoma. After removing the immunoglobulin fraction from t he plasma, his immunoreactive plasma glucagon level returned to normal . Moreover, the immunoglobulin G fraction purified from the patient's plasma inhibited the binding of [I-125]glucagon to rabbit antiglucagon antiserum, OAL-123. Dot-blot analysis demonstrated that the immunoglo bulin G of this patient crossreacted against OAL-123. Therefore, it wa s considered that the prominent hyperglucagonemia in this patient was due to the presence of IgG, which interfered with the measurement of p lasma-immunoreactive glucagon.