Back Blood-tests Explained

Insulin

At a Glance

Why Get Tested?

To help evaluate insulin production by the beta cells in the pancreas; to help diagnose the presence of an insulin-producing tumor in the islet cells of the pancreas (insulinoma); to help determine the cause of low blood glucose (hypoglycemia); to help identify insulin resistance, or to help determine when a type 2 diabetic might need to start taking insulin to supplement oral medications

When to Get Tested?

When you have low blood glucose levels with symptoms such as sweating, palpitations, dizziness, fainting; when you have diabetes and your health practitioner wants to monitor your insulin production; sometimes when it is suspected that you have insulin resistance

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

You may be asked to fast for 8 hours before the blood sample is collected, but occasionally a health practitioner may do the test with, for example, a glucose tolerance test. In some cases, a health practitioner may request that you fast longer.

The Test Sample

What is being tested?

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, the body's main source of energy. Insulin helps transport glucose from the blood to within cells, helps regulate blood glucose levels, and has a role in lipid metabolism. This test measures the amount of insulin in the blood.

Insulin and glucose blood levels must be in balance. After a meal, carbohydrates usually are broken down into glucose and other simple sugars. This causes the blood glucose level to rise and stimulates the pancreas to release insulin into the blood. As glucose moves into cells, the level in the blood decreases and release of insulin by the pancreas decreases.

If an individual is not able to produce enough insulin, or if the body's cells are resistant to its effects (insulin resistance), glucose cannot reach most of the body's cells and the cells starve, while blood glucose rises to an unhealthy level. This can cause disturbances in normal metabolic processes that result in various disorders and complications, including kidney disease, cardiovascular disease, and vision and neurological problems.

Diabetes, a disorder associated with high glucose levels and decreased insulin effects, can be 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.

With insulin resistance, the body is unable to respond to the effects of insulin. The body compensates by producing additional amounts of the hormone. This results in a high level of insulin in the blood (hyperinsulinemia) and over-stimulation of some tissues that have remained insulin-sensitive. Over time, this process causes an imbalance in the relationship between glucose and insulin and, without treatment, may eventually cause health complications affecting various parts of the body.

In addition to type 2 diabetes, insulin resistance may be seen in those with polycystic ovarian syndrome (PCOS), prediabetes or heart disease, metabolic syndrome, and with disorders related to the pituitary or adrenal glands.

Other than in insulin resistance, hyperinsulinemia is most often seen in people with tumor of the islet cells in the pancreas (insulinomas) or with an excess amount of administered (exogenous) 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 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, a person will be asked to fast for 8 hours before blood is collected, but occasionally a health practitioner may do testing when fasting is not possible, such as when a glucose tolerance test (see Glucose) is done. In some cases, the health practitioner may request that a person fast longer than 8 hours.

The Test

How is it used?
When is it ordered?
What does the test result mean?
Is there anything else I should know?

How is it used?

Insulin testing has several possible uses. Insulin is a hormone that is produced and stored in the beta cells of the pancreas. Insulin helps transport glucose , the body's main source of energy, from the blood to within cells. If a person makes too little insulin or is resistant to its effects, cells starve. If someone makes too much, as may happen with an insulin-producing tumor (insulinoma) for example, then symptoms of low blood glucose (hypoglycemia) emerge.

Insulin testing may be used to help:

Diagnose an insulinoma, verify that removal of the tumor has been successful, and/or to monitor for recurrence
Diagnose the cause of hypoglycemia in an individual with signs and symptoms
Identify insulin resistance
Monitor the amount of insulin produced by the beta cells in the pancreas (endogenous); in this case, a C-peptide test may also be done. 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 tests may be ordered when a health practitioner wants to evaluate how much insulin in the blood is made by the body and how much is from outside (exogenous) sources such as insulin injections. The test for insulin measures insulin from both sources while the C-peptide test reflects insulin produced by the pancreas.
Determine when a type 2 diabetic might need to start taking insulin to supplement oral medications
Determine and monitor the success of an islet cell transplant intended to restore the ability to make insulin, by measuring the insulin-producing capacity of the transplant

Insulin testing may be ordered with glucose and C-peptide tests. Insulin levels are also 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.

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 glucose (hypoglycemia) caused by, for example, an insulinoma. Symptoms of hypoglycemia may include:

Sweating
Palpitations
Hunger
Confusion
Blurred vision
Dizziness
Fainting
In serious cases, seizures and loss of consciousness

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

An insulin test may also be done when an individual has or is suspected of having insulin resistance. This may include people with type 2 diabetes, polycystic ovarian syndrome (PCOS), prediabetes or heart disease, or metabolic syndrome.

A health practitioner also may order insulin and C-peptide tests after an insulinoma has been successfully removed to verify the effectiveness of treatment and then order the tests 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:

Disorder	fasting insulin level	fasting glucose level
None	Normal	Normal
Insulin resistance	High	Normal or somewhat elevated
Not enough insulin produced by the beta cells (as seen in diabetes, pancreatitis, for example)	Low	High
Hypoglycemia due to excess insulin (may be seen in insulinomas, Cushing syndrome, excess administration of exogenous insulin, etc.)	Normal or high	Low

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 the 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, these 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 people with type 1 diabetes will also have autoantibodies against insulin.

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