Sugar and metabolism
Insuline
The hormone that lowers blood sugar; measured fasting, a rough measure of insulin resistance, with limited clinical value.
Everything about this testWhat it measures
Insulin is made by the beta cells of the pancreas and makes muscles, liver and fat tissue take up glucose from the blood. If those tissues respond less well to insulin (insulin resistance), the pancreas makes more insulin to keep blood sugar normal; the fasting insulin value then rises while glucose is still normal. Only when the pancreas can no longer keep this up does blood sugar rise and type 2 diabetes develop. The value is always assessed together with the glucose measured at the same moment.
- Increased insulin release as a sign of insulin resistance in overweight, metabolic syndrome or PCOS
- The cause of low blood sugar (hypoglycemia), such as an insulin-producing tumor (insulinoma) or use of insulin or diabetes medicines
- Remaining capacity of the pancreas in known diabetes (in hospital, usually via C-peptide)
High
A raised fasting insulin with a normal glucose fits insulin resistance: the body needs more insulin for the same blood sugar. This mainly occurs with overweight around the belly, little exercise, disturbed fat metabolism (high triglycerides, low HDL), PCOS and during pregnancy. It usually causes no symptoms; it is a risk factor, not a disease. A high insulin with a low glucose is something different and may point to an insulinoma or to use of insulin or sulfonylurea tablets; that belongs with the specialist. Not being fasting, corticosteroids, some antipsychotics and the contraceptive pill also raise the value.
Low
A low fasting insulin with a normal glucose is normal and fits good insulin sensitivity, for example in slim, active people. A low insulin with a high glucose means the pancreas makes too little: that fits type 1 diabetes, long-standing type 2 diabetes or a damaged pancreas. Fasting, heavy exercise and a low-carbohydrate diet lower the value. In people who inject insulin, the measured value says nothing about their own production.
Preparation
- Do not eat anything for 12 hours before the sample is taken and drink only water. After a meal the value is many times higher.
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
The GP assesses a raised insulin together with glucose, weight, blood pressure and fat levels and usually has fasting glucose or HbA1c measured to see whether there is impaired blood sugar or diabetes; an isolated raised insulin does not lead to further testing. With a high insulin combined with low blood sugars, you are referred to an internist (specialist in internal medicine).
Reliability
Fasting insulin is a single value with limited predictive value. Diabetes is diagnosed with fasting glucose, which has fixed cut-off values (the Dutch GP guideline (NHG) on type 2 diabetes mellitus); in known diabetes, HbA1c is monitored. Insulin adds little for detecting diabetes or insulin resistance. The Dutch Society for Clinical Chemistry (NVKC) names as uses the search for an insulinoma or another cause of low blood sugar, and the question of whether someone with diabetes needs insulin. There is no generally accepted cut-off for 'too much' insulin: the measurement is not standardized between laboratories and the spread among healthy people is large. A high value is a sign, not a diagnosis.
Limitations
- The result depends strongly on when you last ate: being strictly fasting (at least 8 to 12 hours) is essential; after a meal the value is many times higher.
- Insulin measurements differ between laboratories and measuring methods, sometimes by tens of percent; reference values are not interchangeable and there is no agreed cut-off value.
- Insulin breaks down quickly: the tube must be processed quickly, and hemolysis (broken red blood cells) falsely lowers the result.
- In people who inject insulin, have antibodies against insulin or use medicines such as corticosteroids, beta blockers or oral contraception, the value is hard to interpret; heavy exercise, lack of sleep, illness and pregnancy also change the value.
How common is this
Insulin resistance is not a registered diagnosis; there are no figures for the Netherlands on how often a raised fasting insulin occurs. However, in 2024 over 1.1 million people with type 2 diabetes were known to their GP (61 per 1,000 inhabitants), and according to the NHG guideline about 30 percent of people over 60 have impaired fasting glucose or impaired glucose tolerance, in which insulin resistance almost always plays a role.
Who is this useful for
With overweight, a raised blood sugar or suspected diabetes, fasting glucose and HbA1c say more than insulin, and an insulin value changes little about that. The result says the most when looking into unexplained low blood sugars, through the specialist. If you have the value measured out of interest, you should know that there is no agreed cut-off value and that a high result does not lead to treatment with medicines; the advice is then the same as for overweight: exercise more, eat healthier, lose weight.
Downsides and risks
- A 'raised' insulin without an agreed cut-off value is quickly labeled online as a disease (insulin resistance), while the result varies a lot and the advice is no different from that for overweight.
- A normal insulin does not rule out disturbed blood sugar; in long-standing type 2 diabetes the value may actually be low.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results