Insulinoma: how reliable is the biochemical evidence?

Background and methods We report a case of insulinoma in which the diagnosis was very challenging as some of the biochemical data were consistently equivocal. In order to assess the relative reliability of the analytical tests, retrospective biochemical data on 45 other cases of histologically confirmed insulinoma were evaluated, enabling the most secure diagnostic process to be identified. Results The data showed that insulin concentrations alone, although measurable, were equivocal in 17% of cases. The addition of C-peptide values clarified the diagnosis in about 50% of the borderline cases, whilst ketone (beta-hydroxybutyrate) concentrations were low during the prevailing hypoglycaemia in all cases. Conclusion The combination of these three tests is suggested as the most effective method for the biochemical diagnosis of hypoglycaemia due to insulinoma.