Fasting Insulin
Insulin is the hormone made by the pancreas that moves glucose from the blood into cells for energy. A fasting insulin test, ordered alongside fasting glucose, helps detect insulin resistance — when cells stop responding well to insulin and the pancreas compensates by producing more.
Normal Range
Fasting: 2–25 µIU/mL (optimal often cited as 2–10 µIU/mL)
Reference ranges may vary slightly between laboratories. Always interpret your result in context with your doctor.
Why is Insulin measured?
Fasting insulin is tested to detect insulin resistance years before fasting glucose or HbA1c become abnormal, evaluate hypoglycaemia, screen for metabolic syndrome, and investigate polycystic ovary syndrome (PCOS).
High Insulin means…
High fasting insulin (above 10–15 µIU/mL) usually indicates insulin resistance. The body is working harder to keep glucose normal. This is a strong early warning sign for type 2 diabetes, fatty liver disease, and cardiovascular risk — often years before glucose itself becomes elevated.
Low Insulin means…
Low fasting insulin can indicate type 1 diabetes (autoimmune destruction of insulin-producing beta cells) or advanced type 2 diabetes where pancreatic function has declined. In non-diabetic adults, low insulin is usually a sign of good metabolic health.
Symptoms associated with abnormal Insulin
When Insulin is high:
- Difficulty losing weight
- Persistent abdominal fat
- Fatigue after meals
- Sugar or carbohydrate cravings
- Skin tags or dark patches (acanthosis nigricans)
- Irregular periods or PCOS symptoms
When Insulin is low:
- Symptoms of type 1 or advanced type 2 diabetes: thirst, frequent urination, unexplained weight loss
How to improve your Insulin
- Replace refined carbohydrates with high-fibre options — fibre slows glucose absorption and reduces insulin demand.
- Resistance training builds muscle, which improves insulin sensitivity more efficiently than cardio alone.
- Time-restricted eating (a 12–14 hour overnight fast) can improve fasting insulin in many people.
- Adequate sleep, low stress, and avoiding late-night eating all measurably lower fasting insulin.
Frequently asked questions about Insulin
What is the HOMA-IR score?
HOMA-IR is calculated from fasting glucose × fasting insulin ÷ 405. A HOMA-IR above 1.9 suggests insulin resistance; above 2.9 is significant. It is a more sensitive marker of metabolic dysfunction than glucose alone.
Can I have insulin resistance with normal blood sugar?
Yes — and this is the most clinically useful insight from a fasting insulin test. Insulin resistance can be present for 5–10 years before glucose rises into the pre-diabetic range. By the time glucose is abnormal, significant metabolic damage may already be done.
Medical Sources
This page is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider about your individual results.