Summary

• Glucose is a sugar that is our main source of energy.
• To be able to use glucose, your body needs insulin. This is a hormone that enables glucose in your blood to enter your body’s cells when it is needed. This helps regulate your blood glucose and keep it at the right level.
• Measuring insulin levels is most often used to investigate the cause of low glucose levels. It can also be used to diagnose insulin resistance.
• It is often used together with a C-peptide test.

What is insulin?

All parts of the body need energy to work. Our main source of energy is glucose. Our body makes glucose from the food we eat and drink. Food molecules are broken down into sugars and absorbed in the small intestine then converted into glucose in the liver and circulated in the blood throughout the body.

To be able to use glucose, your body needs insulin. This is a hormone made in the pancreas, and it enables the glucose in the blood to enter your body’s cells as it is needed. Cells use glucose for energy, or it is stored as glycogen in your liver and muscles for later use.

Low levels of insulin constantly circulate throughout your body. When blood glucose levels rise after a meal, insulin is released by the pancreas and travels in the bloodstream to be used by cells. Humans need insulin daily to survive. Without insulin, glucose cannot leave the bloodstream and enter the body's cells. 

Many of the body’s cells have insulin receptors on their surfaces. When insulin docks on to these receptors, signals are sent inside the cell, and this allows glucose to enter. 

A few hours after a meal, when your cells have taken up all the glucose they need and  blood levels of glucose have fallen, insulin then signals to the liver to store the remaining excess blood glucose. It stores this as carbohydrates and fat.

Insulin works together with glucagon, another hormone made in the pancreas. While the work of insulin lowers blood glucose levels as the cells take up glucose, glucagon's role is to make sure that blood glucose levels don’t fall too low. Low blood glucose can be a serious condition that needs urgent medical treatment.

• If your pancreas makes too much insulin, your glucose levels may fall. Low glucose is known as  hypoglycaemia.
• If your pancreas makes too little insulin, glucose cannot get into your cells. Glucose builds up in your bloodstream until your level is too high. This is known as hyperglycaemia. 

Type 1 and 2 diabetes

If you have diabetes, the glucose - insulin system is not working as it should.

Type 1 diabetes is an autoimmune condition that affects the insulin-making cells in the pancreas and reduces their ability to make insulin. If you have type 1 diabetes you must take insulin to control your blood glucose.

In type 2 diabetes, the insulin you make is not taken up by your cells properly - they do not respond effectively to the insulin signal. This is a condition called insulin resistance. When glucose can't get into your cells, your blood glucose levels rise, and your pancreas tries to compensate by producing more and more insulin. 

Over time, this strains the pancreas. Insulin is made by unique cells in your pancreas called beta cells in an area called the islets of Langerhans.  These cells become damaged and cannot make enough insulin. Eventually, you may need insulin injections.

Gestational diabetes

This can occur during pregnancy and is due to hormones from the placenta interfering with your ability to use or make enough insulin. It can be managed through diet and medication and most people find their glucose levels go back to normal after childbirth. However, it can increase the risk of developing Type 2 diabetes later. See Glucose for more information.

Why get tested?

An insulin test is usually ordered together with a C-peptide test. C-peptide is a byproduct made by the pancreas when it makes insulin. Your pancreas releases about the same amounts of insulin and C-peptide into your bloodstream at the same time. C-peptide doesn't make any difference to your blood glucose levels, but it stays in your blood longer than insulin. This means measuring C-peptide is a more accurate way of working out how much insulin your pancreas is making.

Measuring C-peptide and insulin levels can also be used to tell the difference between insulin that has been produced in your body and insulin that has been injected. This testing can be useful in working out the source of high insulin levels.

C-peptide can be used to diagnose insulin resistance. In this case, the body produces more insulin to compensate for its reduced effectiveness. High C-peptide levels can indicate insulin resistance, and your medical team may recommend lifestyle changes or medications to make your insulin work more effectively.

Measuring glucose, insulin and c-peptide levels together is sometimes used to diagnose hypoglycaemia. Hypoglycaemia can be difficult to diagnose, and it is possible that you may need to be admitted to hospital to allow this to happen safely as part of a 72-hour fast test.

Hypoglycaemia can be caused by taking too much insulin, alcohol consumption, liver disease, kidney disease or an insulinomas (a tumour of the cells in the pancreas) that can produce uncontrolled amounts of insulin and C-peptide. They are almost always benign and can usually be removed with surgery. 

Having the test

Sample

Blood.

Any preparation?

A fasting sample is required.

Your results

Reading your test report

Your results will be presented along with those of your other tests on the same form.  You will see separate columns or lines for each of these tests.

Your medical team will consider your medical history your test results for insulin, glucose, c-peptide and other tests to help make a diagnosis. 

Reference intervals

Your results will be compared to reference intervals (sometimes called a normal range).

• Reference intervals are the range of results expected in healthy people.
• When compared against them your results may be flagged high or low if they sit outside this range.
• Many reference intervals vary between labs so only those that are standardised or harmonised across most laboratories are given on this website.

If your results are flagged as high or low this does not necessarily mean that anything is wrong. It depends on your personal situation. Your results need to be interpreted by your doctor.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help. 

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely. 

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record.

You and your healthcare provider can now access your results whenever and wherever needed. Get further trustworthy health information and advice from healthdirect.