[Differences in insulin secretion facilitate the differential diagnosis of insulinoma and factitious hypoglycaemia]

A 33-year-old female nurse (married; two children; BMI 30.9 kg/m2) had recurrent episodes of symptomatic hypoglycaemia over some months.

Two fasting tests were terminated after 26 hours because the patient became unconscious. Improved insulin/glucose ratio was infinity and 6.1 [mU/l]/[mg/dl] (normal value < 0.5). An hyperinsulinaemic-hypoglycaemic angle "clamp test" produced a C-peptide suppression to minimally 0.26 - 0.38 nmol/l (normal value 0.06 +/- 0.01 nmol). There was no spontaneous or paradoxical burst in insulin or C-peptide concentration after either the fasting or the "clamp test". Serum analysis of sulphonylurea on several occasions documented an increase of glibenclamide above therapeutic range.

The patient denied any intake of oral antidiabetic preparations, but there were no further hypoglycaemia attacks in subsequent months.

The demonstration of sulphonylurea in serum confirmed the diagnosis of factitious hypoglycaemia.

With regard to insulin or C-peptide suppression, the results of the fasting and clamp tests are the same in factitious hypoglycaemia and insulinoma. However, under the influence of sulphonylurea drugs there are no insulin or C-peptide bursts so typical of insulinoma. In case of doubt, detection of sulphonylurea preparations in serum or urine is the only reliable way of diagnosing factitious hypoglaema due to the ingestion of sulphonylurea.