Fasting Insulin

What it is

Insulin is the hormone that helps move sugar out of your blood and into your cells; fasting insulin measures how much of it is circulating after an overnight fast, which can hint at how hard your body is working to keep glucose steady. An important caveat is that insulin tests aren't standardized across laboratories — different labs use different methods and can report meaningfully different numbers for the same sample, so results don't always compare cleanly from one lab to another. It's not part of routine screening for most people and is usually interpreted alongside fasting glucose and HbA1c, in context, rather than as a standalone number.

Typical range

Reference ranges vary between laboratories, and what is normal for you depends on your own history. Your own lab’s range is the one printed on your report.

Worth asking your clinician

• How should I interpret this given that insulin assays vary between labs?
• Does my fasting insulin add anything beyond what my glucose and A1c already tell us?
• If we do follow this over time, should it be from the same lab each time?