What the value means
A fasting insulin of 15 mIU/L (about 90 pmol/L) is still within the reference range of most laboratories, which tends to be very wide – often up to roughly 20–25 mIU/L. Insulin assays are not standardised between laboratories, so results can differ. From a prevention perspective the combination with glucose is informative: the HOMA-IR index = glucose (mmol/L) × insulin (mIU/L) / 22.5. With a glucose of 5.0 mmol/L it comes to about 3.3. HOMA-IR cut-offs vary between studies and populations (a range of roughly 2–3 is often quoted), so it is a rough guide, not a diagnosis. Still, higher insulin with normal glucose can precede a rise in blood sugar by years.
Possible causes
- Abdominal and liver fat – visceral fat and fatty liver are among the most common causes.
- Little physical activity – muscles are the main consumers of glucose; a sedentary routine lowers insulin sensitivity.
- Diet – frequent sweet foods and drinks, refined carbohydrates, late eating shortly before the test.
- Sleep and stress – short sleep and higher cortisol impair insulin sensitivity.
- Hormonal factors – polycystic ovary syndrome, an underactive thyroid, some medicines.
- Incomplete fasting – fewer than 8–12 hours without food falsely raises the value.
What you can do
- Further tests – HbA1c, a lipid profile (triglycerides, HDL), liver tests and, if your doctor advises, a glucose tolerance test.
- Measure your waist – waist circumference is a simple and telling marker of abdominal fat.
- Strength and endurance exercise – combining both improves insulin sensitivity within a few weeks.
- Diet – enough protein and fibre, fewer sugary and processed foods; if you are overweight, modest weight loss helps.
- Sleep – a regular 7–9 hours.
- Follow-up – repeat insulin and glucose in 3–6 months under the same conditions.
When to see a doctor
Discuss the result with your doctor if you are overweight or have high blood pressure, raised triglycerides, fatty liver, irregular periods, a family history of diabetes or HbA1c in the upper range. See a doctor without delay if you have thirst, frequent urination or unexplained weight loss.