Insulin, Plasma

Diagnostic Use

This test can only measure native human insulin.

Insulinoma – The concentration of insulin is disproportionately high in relation to the concurrent low, (<2.5mmol/L) fasting plasma glucose level. See Turner et al. Ideally insulin levels are measured during an hypoglycaemic episode and/or after a carefully supervised 48-72 hour fast.

The secretion of ProInsulin and C-Peptide may also be increased in patients with insulinoma. These assays can be carried out by special arrangement with Endolab.
Tests of insulin suppressability may be undertaken using infusion of insulin and measurement of C-Peptide levels when hypoglycaemic.

Hepatic vein insulin levels can be measured to help localise site of pancreatic islet cell adenoma after selective injections of calcium via branches of the celiac axis artery.
Early diagnosis of diabetes – the first phase of insulin release which occurs 3 to 5 minutes after the intravenous injection of 25g glucose, is absent or blunted. Subsequent insulin secretion may be normal or increased.

A raised fasting insulin value or an excessive response to glucose may suggest insulin resistance such as occurs in obesity, acromegaly, Cushing’s Syndrome, etc.
Note: For clinical purposes the conventional 75g oral glucose tolerance test or 25g IV glucose tolerance test gives adequate information and plasma insulin determinations are generally unnecessary.

R C Turner, N W Oakley and J D N Nabarro, BMJ. 1971: Vol 2, p 132 - 135


Endo/Steroid Lab

Delphic Registration Code



Free Insulin

Turnaround Time

4 days

Test Code