Differential diagnosis of spontaneous hypoglycaemia (see also section on IGF-I).
In some cases of non-islet cell tumour where severe hypoglycaemia is present, IGF-II produced by the tumour has been implicated as the hypoglycaemic agent. The diagnosis is based on an elevated IGF-II to IGF-I molar ratio in association with suppressed insulin, C-peptide, ketones and GH.
Hypoglycaemia, spontaneous or whilst fasting, must first be established by regular monitoring of blood glucose levels. Blood (10 mL) collected in a plain vacutainer or syringe, when the whole blood glucose concentration (confirmed by laboratory analysis) is less than 2.2 mmol/L (or less than 2.5 mmol/L in patients over 60 years), should be used for the tests. Vacutainers (7 mL, red top) may be used for blood collection. Small blood samples from neonates should be transferred to a heparin tube so that the maximum volume of plasma may be collected. A minimum volume of 0.5 mL should be stored at -200C.
Transfer the blood to a plain tube. Separate the serum preferably within 30 min of collection and freeze at -200C. Larger volumes of sample (5 mL) are required for additional studies such as IGF-1 measurements or sulphonylurea identification. Visible haemolysis may invalidate the result.
Send samples to the SAS laboratory. Ensure they remain frozen during transport. Record the blood glucose concentration on the request form.
Follow-up samples (collected during or after treatment) requiring only IGF-II measurements may be sent by first class post.
The SAS Laboratory will provide appropriate reference data and an interpretation of results based on relevant biochemical and clinical information.
Centre offering this assay
Guildford RSH Peptide Hormone Laboratory.
Marks V, Teale JD. Tumours producing hypoglycaemia. Diabetes/ Metabolism Revs. 1991; 7: 79-91.