Biomarker · Metabolic
Fasting insulin
Fasting insulin shows how much insulin your body needs to keep glucose stable overnight. Learn how it relates to insulin resistance and its limitations.
Written by LON6EVITY Editorial Team · Last updated
Overview
Insulin is a hormone made by the pancreas that helps glucose move from the blood into cells. A fasting insulin test measures insulin levels after an overnight fast.
Why it matters
In insulin resistance, cells respond less well to insulin, so the pancreas produces more to keep glucose normal. NIDDK explains that insulin resistance can be present for years before blood glucose rises into the prediabetes range.
Limitations
Insulin assays are not fully standardised between laboratories, and there is no universally agreed 'normal' cut-off. Fasting insulin is not a routine screening test in most guidelines and is best interpreted together with glucose and clinical context.
How the test is performed
A blood sample after an 8-hour fast, often alongside fasting glucose.
Reference ranges
Reference ranges and targets differ between laboratories, units and guidelines, and depend on age, sex, method and your overall clinical picture. A single result is not a diagnosis — interpret it with a qualified clinician.
Factors that can affect the result
- Fasting status
- Body weight and abdominal fat
- Physical activity
- Medications including insulin
Questions people commonly ask
- Can fasting insulin diagnose insulin resistance?
- There is no single diagnostic cut-off. Clinicians look at insulin together with glucose, triglycerides, waist circumference and other findings.
Related biomarkers
Related topics
Understand your biomarkers in context
What does this mean for your own health data? Log your results, follow trends over time and bring an organised summary to your next doctor's appointment.
Sources
- Insulin in Blood. MedlinePlus, U.S. National Library of Medicine.
- Insulin Resistance & Prediabetes. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).