Diagnosis of self-induced hyperinsulinism in an insulin-dependent diabetic patient by radioimmunoassay of free C-peptide.
On the basis of results of simultaneous determinations of plasma free insulin and free c-peptide, episodes of hypoglycemia in an insulin-dependent diabetic were attributed to surreptitious self-administration of insulin. Immunoreactive c-peptide values were falsely increased and diagnostically misleading when measured in unextracted plasma. After preliminary removal of antigen/antibody complexes from the plasma by extraction with polyethylene glycol, the c-peptide values, referred to as "free c-peptide," were suppressed. We suggest that insulin antibodies formed complexes with proinsulin-like material in the plasma of this patient, which accounted for most of the c-peptide immunoreactivity in her unextracted plasma. These complexes must be removed if c-peptide measurements are to be accurate.
D000293:Adolescent; D002096:C-Peptide / Q000097:blood*; D048909:Diabetes Complications; D003920:Diabetes Mellitus / Q000188:drug therapy; D005260:Female; D006801:Humans; D006946:Hyperinsulinism / Q000097:blood / Q000175:diagnosis* / Q000209:etiology; D007328:Insulin / Q000627:therapeutic use; D010455:Peptides / Q000097:blood*; D011863:Radioimmunoassay; D012651:Self Medication / Q000009:adverse effects
D002096:C-Peptide; D007328:Insulin; D010455:Peptides