Introduction: Insulinoma a neuroendocrine tumour is diagnosed by inappropriately raised Insulin concentrations during a spontaneous or induced episode of hypoglycaemia. A provocative 72-h supervised fast is done to evaluate suspected inappropriate insulin secretion. Our aim is to see if it is feasible for a shorter duration of fast is enough to confirm Insulinoma.
Method and results: In our Trust we analysed retrospectively in the last 10 years, patients who had prolonged 72 h fast for suspected Insulinoma. 41 patients underwent prolonged (72 h) supervised fast between 2008 and 2017. The time taken to reach significant hypoglycaemia (venous glucose <2.2 mmol/l) was noted. Of the 41 patients, 3 had a positive test confirmed by inappropriately raised Insulin, pro-insulin and c-peptide levels. 2 patients had a positive test within 24 h and 1 within 48 h. The rest of 38 patients were evaluated for reactive hypoglycaemia.
Discussion: All patients who had a positive result developed significant hypoglycaemia mostly within 24 to 48 h of starting the fast. Our numbers were modest due to the rare nature of the disease. We are all aware of the NHS bed pressures and the need for specialist units to do these tests and in the presence of modern parameters like pro-insulin and insulin levels to measure we suggest a 48-h supervised fast to confirm insulinoma. This will be more cost effective and lead to early diagnosis and management.