Insulin (Fasting)

What is fasting insulin?

Insulin is the hormone secreted by the beta cells of the pancreas that allows sugar (glucose) in the blood to enter the cells. Its secretion increases when blood sugar rises after a meal, and during fasting it falls to a low level that meets the body's basic needs. By regulating energy storage in the liver, muscle and fat tissue, it helps keep blood sugar within a narrow range.

The fasting insulin test measures the amount of insulin in the blood after an overnight fast and reflects the pancreas's insulin production at rest. The result is usually evaluated together with fasting blood glucose measured at the same time; from these two values, an insulin resistance index called HOMA-IR can be calculated. The measurement is performed on serum using immunological methods, and the result is reported in µIU/mL.

When is the fasting insulin test ordered?

Your doctor most often orders this test when insulin resistance, a condition in which the body does not respond adequately to insulin, is suspected. Because insulin resistance can progress for a long time without disturbing blood sugar, fasting insulin can provide an early clue even while blood sugar is still normal. In recurrent episodes of low blood sugar, it is used together with C-peptide and blood sugar to investigate the source of the problem.

• Fat accumulation around the waist, difficulty losing weight and frequent hunger
• Darkened, velvety patches of skin on the neck and in the armpits (acanthosis nigricans)
• Evaluation of polycystic ovary syndrome (PCOS)
• A history of gestational diabetes, prediabetes, or a family history of type 2 diabetes
• Metabolic syndrome, fatty liver or high triglycerides
• Unexplained episodes of low blood sugar

How do you prepare for the fasting insulin test?

This test requires 8–12 hours of fasting; usually nothing is eaten after dinner and blood is drawn the next morning. During the fast you may drink only water; tea, coffee, fruit juice, chewing gum and smoking can affect the result. Fasting for much longer than twelve hours can also lower the values, so sticking to the recommended duration gives the most accurate result.

Cortisone, some diabetes medications and hormone therapies can affect insulin levels; do not stop your medications on your own, but say which ones you take when the sample is collected. If you use insulin injections, be sure to mention this, because the measured value may also reflect the injected insulin. High-dose biotin supplements can also affect the measurement method. With a Curavita nurse coming to your home early in the morning, you can have blood drawn from a vein in your arm without prolonging your fast or having to travel anywhere.

What does the fasting insulin result mean?

High fasting insulin may suggest that the pancreas is working harder than usual to keep blood sugar normal and that insulin resistance is present. This picture may be accompanied by excess weight, a sedentary lifestyle, polycystic ovary syndrome, pregnancy and medications such as cortisone; less commonly, Cushing's syndrome, acromegaly or an insulin-secreting tumor (insulinoma) may be the cause. In insulinoma, high insulin is seen together with low blood sugar at the same time.

Low fasting insulin can occur naturally during prolonged fasting, but it can also be found in type 1 diabetes or in advanced type 2 diabetes, when the pancreas can no longer produce enough insulin. There is no single threshold for insulin resistance that every laboratory accepts; for this reason, the result is interpreted together with blood sugar, HbA1c and other findings. Reference ranges may vary by laboratory, age and sex; the range of the laboratory that performs the test is stated on this page. Your doctor, who evaluates your symptoms and other tests together, can tell you what your fasting insulin result means for you.