Test Background Proinsulin is cleaved to form connecting peptide (C-peptide) and insulin prior to secretion into the portal circulation. Insulin is integral to carbohydrate and fatty acid metabolism with utility in cellular glucose uptake, increased glycogen synthesis, enhanced triglyceride turnover and fatty acid esterification in the adipose tissue. Insulin also mediates reduced gluconeogenesis and lipolysis, increased potassium re-uptake, arterial vasodilation and diminished protein catabolism.
Clinical Indications Evaluation of fasting hypoglycaemia β-cell tumours or factitious causes, eg. abuse of sulphonylureas/exogenous insulin Assessment of fasting insulin resistance in PCOS
Reference Range Fasting: 3-15 mIU/L
Sample Required SST (gold top) or serum (red top) on ice rush to laboratory
Collect into tube on ice, separate in a chilled centrifuge and freeze immediately.
Sample Volume 1 mL
Transport/Storage Send to lab frozen.
Turnaround Time 1 week
Notes Grossly haemolysed samples are unsuitable for this assay.