INAPPROPRIATELY ELEVATED PLASMA INSULIN‐LIKE GROWTH FACTOR II IN RELATION TO SUPPRESSED INSULIN‐LIKE GROWTH FACTOR I IN THE DIAGNOSIS OF NON‐ISLET CELL TUMOUR HYPOGLYCAEMIA

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Abstract
The diagnosis of non-islet cell tumour (hypoinsulinaemic) hypoglycaemia has been complicated by contradicatory biochemical evidence. Although insulin-like growth factor II (IGF-II) has been identified as the hypoglycaemic agent, plasma levels are often not elevated. In this study specific radioimmunoassay procedure for the measurements of IGF-I and IGF-II are described. Reference data on plasma IGF-II concentrations in relation to a wide range of IGF-I levels have been accumulated using plasma samples from acromegalic, hypopituitary and insulinoma (i.e. hyperisulinaemic hypoglycaemia) patients as well as normal subjects from all age groups. The reference data indicate that a low plasma IGF-I value is normally associated with a relatively low plasma IGF-II level. Within a group of hypoinsulinaemic hypoglycaemia patients, a small number, invariably with evidence of a neoplasm, had low plasma IGF-I concentrations but apparently normal IGF-II levels. We propose that, in such cases, an apparently normal plasma IGF-II value is inappropriately high for the low plasma IGF-I level and, in association with non-ketotic hypoinsulinaemia and suppressed plasma growth hormone (GH), is diagnostic of a non-islet cell tumour as the cause of hypoglycaemia.