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Fasting Insulin

Published: July 27, 2026Updated: August 25, 2026

Fasting insulin measures the amount of insulin in your blood after an overnight fast, providing insight into your body's insulin production and sensitivity.

Quick summary

Fasting insulin test evaluates insulin levels in the blood after an overnight fast.

Medically reviewed by WellAlly Editorial TeamLast reviewed August 25, 2026Editorial policy

Key facts at a glance

Units
μIU/mL
Clinical utility
diagnostic
Result kind
quantitative
FDA-cleared
Roche Insulin, Abbott Insulin, Siemens Insulin, Mercodia Insulin
interpretation: {"text":"Fasting insulin levels between 2.6–24.9 μIU/mL indicate typical insulin production and sensitivity.","label":"Normal"}; {"text":"Levels above 24.9 μIU/mL may suggest insulin resistance or other conditions affecting insulin production.","label":"Elevated"}

Fasting insulin is a blood test that measures the concentration of insulin in your bloodstream after an overnight fast. This biomarker is crucial for assessing how well your body produces and uses insulin, a hormone that regulates blood sugar levels.

Typically, insulin levels are low when fasting, as the body should not need to produce much insulin to manage blood sugar. Elevated fasting insulin levels can indicate insulin resistance, a condition where cells do not respond well to insulin, often preceding type 2 diabetes.

The reference range for fasting insulin is generally between 2.6 and 24.9 μIU/mL. Levels above this range may suggest insulin resistance, while levels below may indicate issues with insulin production, such as in type 1 diabetes.

Frequently asked questions

What is the purpose of a fasting insulin test?
The test assesses insulin production and helps diagnose insulin resistance or diabetes.
How is fasting insulin different from fasting blood glucose?
Fasting insulin measures the hormone directly, while fasting blood glucose measures sugar levels, providing complementary information.
  1. 1
    American Diabetes Association: Insulin ResistanceSource
  2. 2
    Mayo Clinic: Insulin TestsSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 25, 2026. · Read our editorial policy