[Hypoglycemia in nondiabetic patients: When is the 72-hour-fast test required and how can it be interpreted?]

Whereas hypoglycaemia is uncommon in nondiabetic patients, it is a frequent reason for consultation. Hypoglycaemia is confirmed when criteria of Whipple's triad are fulfilled. If a venous sample cannot be collected when hypoglycemia occurs spontaneously, a 72-hour-fast test should be performed firstly to affirm the reality of hypoglycaemia and secondly to make the etiological diagnosis. Before carrying out this long and expensive test, the obvious causes of hypoglycaemia must be ruled out: iatrogenic, severe prolonged undernutrition, liver or renal deficiency, adrenal insufficiency, IGFII or pro-IGFII secreting tumours…At the time of hypoglycemia, plasma insulin≥3mUI/L, C-peptide≥0.6ng/mL, proinsulin≥5pmol/L associated with plasma beta-hydroxybutyrate≤2700μmol/L provide evidence for inappropriate insulin secretion. The lack of hypoglycaemia after a 72-hour-fast test rules out, in the majority of cases, organic hypoglycaemia.