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Insulin Test

Formal name: Insulin

Related tests: C-Peptide, Glucose, Glucose Tolerance Test (GTT)

At a Glance

Why get tested?

To help evaluate insulin production, diagnose an insulinoma, and to help determine the cause of hypoglycemia.

When to get tested?

When you have documented hypoglycemia, when you have symptoms suggesting insulin either is being inappropriately released or utilized by your body;  when you have diabetes and your doctor wants to monitor your insulin production; sometimes to document insulin resistance.

Sample required?

A blood sample drawn from a vein in your arm

The Test Sample

What is being tested?

This test measures the amount of insulin in the blood. Insulin is a hormone that is produced and stored in the beta cells of the pancreas. It is vital for the transportation and storage of glucose at the cellular level, helps regulate blood glucose levels and has a role in lipid metabolism.

When blood glucose levels rise after a meal, insulin is released to allow glucose to move into tissue cells, especially muscle and adipose (fat) cells, where is it is used for energy production.  Insulin then prompts the liver to either store the remaining excess blood glucose as glycogen for short-term energy storage and/or to use it to produce fatty acids. The fatty acids are eventually used by adipose tissue to synthesize triglycerides to form the basis of a longer term, more concentrated form of energy storage. 

Without insulin, glucose cannot reach most of the body’s cells. Without glucose, the cells starve and blood glucose levels rise to unhealthy levels. This can cause disturbances in normal metabolic processes that result in various disorders including kidney disease, cardiovascular disease, vision and neurological problems. Thus, diabetes, a disorder associated with decreased insulin effects, is eventually a life-threatening condition.

People with type 1 diabetes produce very little insulin and so eventually require insulin supplementation therapy. Type 2 diabetes is generally related to insulin resistance, which increases with time. People with type 2 diabetes may initially be managed only with lifestyle modifications such as diet and exercise. Eventually, they may require oral medications that increase the sensitivity of their body’s cells to insulin or that stimulate their body to produce more insulin. Type 2 diabetics may also eventually need to use insulin injections to achieve normal glucose levels. 

Insulin resistance may also be seen in those with polycystic ovarian syndrome (PCOS), pre-diabetes or heart disease, metabolic syndrome, and with disorders related to the pituitary or adrenal glands.

Insulin and glucose levels must be in balance. Hyperinsulinemia is an excess amount of insulin in the blood. Other than in insulin resistance, this is most often seen in people with insulinomas or with an excess amount of administered insulin. Hyperinsulinemia causes low blood sugar  (hypoglycemia), which can lead to sweating, palpitations, hunger, confusion, blurred vision, dizziness, fainting and seizures. Since the brain is totally dependent on blood glucose as an energy source, severe glucose deprivation due to hyperinsulinemia can lead fairly quickly to insulin shock and death.

How is the sample collected for testing?

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

Is any test preparation needed to ensure the quality of the sample?

Typically you will be asked to fast for 8 hours before blood is collected but occasionally your doctor may do it at other times such as when a glucose tolerance test is done. In some cases your doctor may request that you fast longer.

The Test

How is it used?

Insulin may be used, along with glucose and C-peptide levels, to help diagnose insulinomas and to help diagnose the cause of documented acute or chronic hypoglycemia. Insulin and C-peptide levels may also be used to monitor the amount of endogenous insulin produced by the beta cells, to check for insulin resistance, and to help determine when a type 2 diabetic might need to start taking insulin to supplement oral medications.

Insulin levels are sometimes used in conjunction with the glucose tolerance test (GTT). In this situation, blood glucose and insulin levels are measured at pre-established time intervals to evaluate insulin resistance, particularly in obese individuals.

When is it ordered?

Insulin levels are most frequently ordered following a low glucose and/or when someone has acute or chronic symptoms of  low blood sugar (hypoglycemia), such as

• Sweating

• Palpitations

• Hunger

• Confusion

• Blurred vision

• Dizziness

• Fainting

• In serious cases, seizures

These symptoms can indicate low blood glucose but can also be seen with other conditions.

Insulin and C-peptide are produced by the body at the same rate as part of the conversion of proinsulin to insulin in the pancreas. Both may be ordered to evaluate how much insulin in the blood is made by the body (endogenous) and how much is from exogenous sources. The test for insulin measures insulin from both sources while the C-peptide test reflects insulin produced by the pancreas (endogenous insulin).

A doctor also may order both tests to verify that an insulinoma has been successfully removed and periodically to monitor for recurrence. Periodic testing may also be used to monitor the success of an islet cell transplant by measuring the insulin-producing capacity of the transplant.

What does the test result mean?

Insulin levels must be evaluated in context.

Results seen:

Elevated insulin levels are seen with:

• Acromegaly

• Cushing syndrome

• Use of  drugs such as corticosteroids, levodopa, oral contraceptives

• Fructose or galactose intolerance

• Insulinomas

• Obesity

• Insulin resistance, such as appears in type 2 diabetes and metabolic syndrome

Decreased insulin levels are seen with:

• Diabetes

• Hypopituitarism

• Pancreatic diseases such as chronic pancreatitis (including cystic fibrosis) and pancreatic cancer

Is there anything else I should know?

Insulin for injection used to come strictly from animal sources (cow and pig pancreas cells). Most insulin used today is synthetic, made by biochemical synthesis to identically match the biological activity of insulin produced by human cells.

There are different pharmaceutical formulations of insulin with different properties. Some are rapid-release and quick-acting and others are slow-release preparations that act over a prolonged period. Diabetics may take mixtures and/or different types of insulin throughout the day.

Insulin assays are designed to measure endogenous human insulin. However, different assays react variably with exogenous (animal or synthetic) insulin. If someone is receiving insulin, these effects should be clarified with the testing laboratory. If  several or periodic insulin assays will be performed they should be analyzed by the same laboratory to ensure consistency.

The insulin tolerance test (ITT) is not widely used, but is one method for determining insulin sensitivity (or resistance) especially in obese individuals and those with PCOS. This test involves an IV-infusion of insulin, with subsequent measurements of glucose and insulin levels.

If someone has developed antibodies against insulin, especially as a result of taking non-human (animal or synthetic) insulin, they can interfere with  insulin testing. In this case a C-peptide may be performed as an alternative way to evaluate insulin production. Note also that most persons with type I diabetes will also have autoantibodies against insulin.

Common Questions

Can I do an insulin test at home?

No. Although glucose levels can be monitored at home, insulin tests require specialized 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 because it is a protein and is broken down in the stomach before it can be absorbed.

How is an insulinoma treated?

Insulinomas are insulin-producing tumors that are usually benign. They are typically treated by being located and removed.  Once removed, generally they do not return.

What else is important about insulin resistance?

Insulin resistance is a warning signal that the body is having problems processing glucose, and it is characteristic of pre-diabetes.  Patients with early or moderate insulin resistance often don’t have any symptoms, but if their condition is ignored, it puts them at a much greater risk of developing type 2 diabetes, hypertension, hyperlipidemia, and/or heart disease several years down the road. Abdominal obesity, insulin resistance, dyslipidemia, and hypertension form a set of risk factors that are referred to as the metabolic syndrome.

Risk factors for insulin resistance include:

• Obesity, especially abdominal obesity

• Family history of diabetes or insulin resistance

• Gestational diabetes

• Polycystic ovary syndrome

Treatment of insulin resistance involves changes in diet and lifestyle.  The American Diabetes Association (ADA) recommends losing excess weight, getting regular amounts of moderate intensity physical activity, and increasing dietary fiber to lower blood insulin levels and increase the body’s sensitivity to it.

Content last reviewed in April 2010. | This page was last modified in January 2011.