At a glance

Why get tested?

To help evaluate insulin production in diabetes, diagnose an insulinoma (insulin-producing tumour), and to help determine the cause of low blood glucose (hypoglycaemia)

When to get tested?

If you have hypoglycaemia, if you have symptoms suggesting insulin is being inappropriately produced by your body, and sometimes if you have diabetes and your doctor wants to monitor your insulin production

Sample required?

A blood sample drawn from a vein in your arm

What is being tested?

Insulin is a hormone that is produced by the pancreas. Insulin helps to control blood glucose levels and plays a role in controlling the levels of carbohydrates and fats stored in the body.

When blood glucose levels rise after a meal insulin is released by the pancreas. The insulin allows glucose to be taken up by the body's cells, especially muscle cells, where is it is used for energy production. Insulin then signals to the liver to store the remaining excess blood glucose as carbohydrates and fat.

Humans need insulin on a daily basis to survive. Without insulin, glucose cannot leave the bloodstream and enter most of the body's cells. The cells starve and blood glucose levels rise to dangerous levels. Eventually, very high glucose levels lead to a life-threatening condition called a diabetic coma.

People with type 1 diabetes produce very little insulin and must take insulin injections several times a day. People with type 2 diabetes usually can produce insulin and their insulin levels may even be high, but the body is not able to respond normally to the insulin. This is known as insulin resistance. People with type 2 diabetes may need oral medications that increase their body's cells response to insulin or that stimulate their body to produce more insulin. In some cases type 2 diabetics may also need to take insulin injections to keep their blood glucose levels normal.

Insulin and glucose levels must be in balance. An excess amount of insulin in the blood is known as 'hyperinsulinaemia'. If this is caused by an insulin-producing tumour in the pancreas (a so-called 'insulinoma') or due to an excess amount of injected insulin, it can be very dangerous. It causes hypoglycaemia (low blood glucose levels), which can lead to sweating, rapid heart beat, hunger, confusion, visual problems and seizures. Since the brain is totally dependent on blood glucose as an energy source, glucose deprivation due to hyperinsulinaemia can lead to death.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

The Test

How is it used?

Insulin levels are used to diagnose insulin resistance, which means the body is not responding normally to insulin and the blood glucose level may be raised (hyperglycaemia). Insulin levels are sometimes measured as part of a glucose tolerance test (GTT).

Insulin levels may also be used, often along with C-peptide levels, to help diagnose the cause of low blood glucose (hypoglycaemia), such as an insulinoma.

When is it requested?

Insulin levels are most frequently requested following an abnormal glucose test and/or when a patient has short- or long-term symptoms of low blood glucose (hypoglycaemia), such as sweating, palpitations, hunger, confusion, visual problems and seizures (although these can be caused by other conditions).

Insulin and C-peptide are produced by the body at the same rate. Both may be requested to evaluate how much insulin in the blood is due to endogenous production (what your body is making) and how much is from exogenous (produced outside the body, e.g. injected) sources. Insulin tests will reflect the total of endogenous and exogenous insulin, while C-peptide will reflect only the endogenous insulin.

Your doctor also may request both tests to check that an insulinoma has been successfully removed.

If you are one of the few people who have received a pancreas cell transplant to restore your ability to produce insulin, your insulin level may be monitored to determine whether or not this procedure is successful over time.

What does the test result mean?

Insulin levels must be evaluated in context. If fasting insulin and glucose levels are normal, most likely the body's glucose regulation system is functioning normally. If insulin is raised and glucose is normal and/or moderately raised, then there may be some insulin resistance, as in type 2 diabetes. If the insulin is low and the glucose is high, then most likely there is insufficient insulin being produced by the body, as in type 1 diabetes. If insulin levels are normal or raised and glucose levels are low, then the patient is hypoglycaemic due to excess insulin, such as due to a tumour in the pancreas that produces insulin, a so-called insulinoma.

About Reference or “Normal” Ranges

Common Questions

Can I do an insulin test at home?

No.  Although glucose levels can be monitored at home, insulin tests require specialised instruments and training.

Why does insulin have to be injected?

Insulin must be injected or given via an insulin pump.  It cannot be given orally (by mouth) because it breaks down in the stomach.

How is an insulinoma treated?

Insulinomas are insulin-producing tumours but are most often not malignant. They are usually treated by being located and removed. Once removed, generally they do not return.

What is insulin resistance?

Insulin resistance means the cells of the body are not responding normally to insulin and are not able to take up glucose from the bloodstream normally. The pancreas tries to compensate by producing more insulin. This results in elevated levels of insulin and C-peptide in the blood along with normal or elevated glucose levels. Glucose, insulin and C-peptide levels may help your doctor diagnose this condition.

Insulin resistance can be part of the so-called metabolic syndrome, seen in people with obesity, high blood pressure and high lipid levels (hyperlipidaemia). In young women this is also associated with polycystic ovary syndrome. Insulin resistance may develop into type 2 diabetes. 

Treatment of insulin resistance involves changes in diet and lifestyle. Diabetes Australia recommends losing excess weight and getting regular amounts exercise to lower blood insulin levels and increase the body’s sensitivity to insulin.

Last Review Date: July 9, 2014