Insulin Testing - General Guidelines

Insulin is a hormone produced in the pancreas that’s used to transport glucose throughout the body. As we eat, carbohydrates are processed into sugar, or “glucose” which is then absorbed by cells for energy. Insulin testing is used to determine levels within the body, and a “fasting insulin”, or “serum” may be ordered by a health practitioner. Blood drawn from an individual, (usually after fasting for at least 8 hours) is sent to a lab for analysis and can provide many insights into a person’s pancreatic health and insulin function. Other related tests, such as the “C-peptide” which monitors insulin made only in the pancreas, and “glucose tests”, used to detect diabetes are also sometimes ordered in addition to “insulin testing”.

There are nearly 400 medications (both prescription and over-the-counter) that can affect blood glucose levels. Aspirin, corticosteroids, estrogen, diuretics, anti-seizure medications, and some antidepressants tend to raise glucose levels, while insulin, oral hypoglycemic medications, anabolic steroids, and acetaminophen have the opposite effect, lowering glucose in the bloodstream. Heavy physical activity or exercise directly prior to insulin testing can affect blood glucose levels as well.

Why Test Is Used

While insulin is produced and stored in beta cells within the pancreas, there are a number of medical conditions that can interfere with its ability to effectively carry out the glucose transfer process. If too little insulin is produced, or if the body is resistant to its effects, cells will starve. If too much is available, low blood glucose may result.

Insulin testing may be used to help indicate:

• Pancreatic tumors that produce insulin, known as “insulinomas”
• Whether tumor removal has been successful/recurrent
• Insulin resistance (cells do not use glucose efficiently)
• Insulin created solely in the pancreas
• When type II diabetes escalates and insulin is necessary
• The success of an islet cell transplant (meant to restore insulin producing capability)

Testing may also be done when blood glucose levels are low and/or
chronic/acute symptoms of hypoglycemia exist that include:

• Perspiring
• Palpitations
• Hunger
• Confusion
• Vision disturbance
• Dizziness
• Fainting
• Seizures

How does it work?

In healthy individuals, the correct amount of insulin is produced in the pancreas, allowing for proper glucose transport and absorption by the cells. Sometimes however, this system breaks down, leading to medical conditions that require management or treatment. Reasons for this may include lifestyle choices, such as poor diet and inactivity, or an underlying disease process. Because blood glucose levels increase after consuming food, insulin testing may require fasting for several hours before blood can be drawn. C-peptide, glucose testing, or glucose tolerance testing, that requires blood drawn at intervals may be ordered for individuals as well.

About Results

A fasting insulin test is generally measured in micro units per milliliter.

Normal levels while fasting are 5-20 mcU/mL. Results may vary slightly per laboratory.

High fasting insulin levels could signal insulin resistance, while low insulin levels may point to diabetes or pancreatitis. Conditions seen in both normal or high fasting insulin levels include insulinomas, Cushing syndrome, or excess outside insulin.