Insulin

5 mL blood in EDTA (preferred) or a plain tube; must be separated and frozen immediately.

Simultaneous plasma glucose levels are required for interpretation.

Immunoassay.

<5 mU/L during hypoglycaemia; 4-10 mU/L after 8 hour fast, and with a normal plasma glucose.

Investigation of fasting hypoglycaemia and insulin resistant states.

Neither insulin nor C-peptide assays are of value in the interpretation of a GTT.

Increased levels and increased insulin/glucose ratios are found with pancreatic islet beta cell hyperplasia or insulinomas.

Non-insulin dependent diabetes mellitus and insulin therapy may also give high levels.

To identify self-administration of insulin as a cause of hypoglycaemia, C-peptide assay is also required. See C peptide.