Endocrine Abstracts

Insulinoma causes fasting hypoglycemia due to inappropriate insulin secretion. The diagnosis of insulinoma is based on Whipple’s triad (1. symptoms precipitated by fasting with 2. associated blood sugars of 50 mg/dl or less and 3. relief of symptoms by glucose administration) during a supervised 72 h fasting test. After introducing reliable assays for measurement of insulin and proinsulin, there is an ongoing debate whether a 48 h fasting test is sufficient for diagnosis or a 72 h fast is necessary to detect patients with insulinoma. The aim of our study was to evaluate the positive fast within 48 h in a large series of patients with insulinoma.

In a retrospective study (1970–2004) we identified 39 patients (24 females, 15 men; average age 47 years [range 12–78 years]) with insulinoma. Surgical pathology confirmed the diagnosis in 34 cases: 24 patients had a benign tumour, 4 had malignant insulinoma and 6 patients had multiple endocrine neoplasia type 1. The average body mass index (BMI) was 28.5 (range 17.3–39.1). 16 patients were diagnosed by spontaneous hypoglycaemia. 23 patients were tested with a 48 h fasting test.

The fast was terminated due to neuroglycopenic symptoms in 4 patients (17.4%) by 12 h, in 17 patients (73.9%) by 24 h, and in 22 patients (95.7%) by 48 h. One patient had no neuroglycopenic symptoms, but was diagnosed by glucose and insulin levels during the 48 h fast.

In conclusion, the 48 h fasting test was successful in the diagnosis of insulinoma in our patient cohort, especially if even subtle signs of neuroglycopenia were recognized by the medical personnel. In this series we did not observe a need for fasting beyond 48 h, and we therefore established the 48 h fasting test as standard protocol resulting in cost reduction.