Test Identifier Information
Roche Cobas e411 after PEG precipitation of immunoglobulins.
|Diagnostic Use / Indications|
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
|External Price||$33.36(Exclusive of GST)|
Simultaneous glucose levels are needed to interpret results.
Patients with suspected insulinoma should be fasted for 15 – 18 hours prior to sampling for plasma insulin and glucose, provided blood sugar values allow this. If possible, blood should be drawn for insulin and C-peptide as well as glucose when spontaneous hypoglycaemia occurs – since such measurements can be diagnostic in insulinoma.
The results of concurrent plasma blood glucose determinations must be sent with the samples for insulin assay, as isolated plasma insulin values are meaningless.
Biguanides, sulphonylurease and β blocking drugs should be discontinued prior to testing.
Does not measure Lispro insulin.
|Patient Specimen||Blood 2 mL EDTA or Plain . No haemolysis!|
|Paediatric Specimen||Blood 0.6 mL EDTA or Plain (must get 0.3 mL plasma or serum)|
|Sample Delivery to Lab||Whole blood should be kept in an ice/water mixture.|
Instructions for Referral to CHLabs
|Aliquot Instructions||Minimum 0.3 mL Plasma or Serum. Preferably >0.5 mL Plasma or Serum. No hemolysis! Freeze.|
|Aliquot Transport to CHL||Frozen (preferrably), otherwise in ice/water mixture.|
|Contact Phone Number||(03) 364 0884 | x80884|
|Test Availability||Mon - Fri, business hours only|
|Turnaround Time||1 - 4 days|
10 - 80 pmol/L (after overnight fast, adult, BMI < 25)
Raised values (ie increased insulin/glucose ratio):
Obesity, insulinoma, Cushing’s Syndrome, Acromegaly, sulphonylurease, sex steroids, amino acids, glucagon and gut hormones, β blocking drugs, insulin receptor abnormalities.
In the presence of normal or elevated plasma glucose, raised fasting insulin suggests insulin resistance.
If patient hypoglycaemic, an elevated fasting insulin is suggestive of inappropriate insulin excess secondary to endogenous hypersecretion, sulphonylurea use or exogenous insulin administration.
Low values (ie decreased insulin/glucose ratio):
Diabetes mellitus, hypokalaemia, phaeochromocytoma, restricted carbohydrate intake, β-blocking drugs, hypoglycaemia, streptozotocin, somatostatin.
|Uncertainty of Measurement|
±3 pmol/L at < 34 pmol/L.
±7% at > 34 pmol/L.
Measure glucose at the same time.
In the complete absence of hemolysis, insulin in EDTA plasma or serum is stable for 24 hours at room temperature. However since hemolysis is common in routine clinical samples we recommend transporting samples at 0o (in ice/water mixture) or frozen.
Insulin is very sensitive to even slight hemolysis and the effect increases with temperature and time. For example, hemolysis at a level of 1.3g Hb/L immediately lowers insulin by 10%. And at 0.4g Hb/L, 1 hour at room temperature lowers insulin by 10%.
This test can only measure native human insulin. Animal samples, including dogs, are not acceptable as there is little cross-reaction with the differing amino-acid sequences. Similarly, we cannot measure modified human insulins (insulin analogues) such as lispro insulin.
|Delphic Number Test Number||6533|