ABSTRACT
In a 57-year-old man with symptomatic hypoglycaemias which gave cause to suspect an insulinoma, normal insulin levels were initially found. A repeated fasting assay at another hospital did, however, reveal the expected hyperinsulinaemia. Scans revealed an abnormality in the pancreas. After surgical removal of the insulin-producing tumour the patient made a quick recovery. The diagnosis of organic hyperinsulinaemia is established by demonstrating inappropriately high serum-insulin concentrations during fasting hypoglycaemia. The diagnostic normative values are based on the classic polyclonal method of determination. This new highly-specific insulin assay has no cross-reactivity with pro-insulin, which is often produced disproportionately more by an insulinoma. As a result of this false-normal insulin values are found. Therefore new normative values are needed for the newer insulin assays when diagnosing an insulin-producing islet cell tumour. Pro-insulin and C-peptide assays may play a useful role in this.
