What is a fasting Insulin Test?

The insulin blood test is also known as the fasting insulin, insulin serum, or total and free insulin test. The fasting insulin test determines the insulin levels in the body after a period of fasting. Insulin is an anabolic hormone secreted by the beta cells of the pancreas and regulates the uptake of glucose, the main source of the body’s energy, from the bloodstream to the cells. Insulin helps maintain glucose within the normal ranges. Too high or too low levels of insulin in the body can be equally harmful and can result in hypoglycemia and hyperglycemia, respectively.

What is the fasting insulin test used for?

The insulin test is used to determine the reason for low blood sugar, monitor insulin resistance, monitor people with type 2 diabetes mellitus, the presence of insulinoma – a tumour on the pancreas, and also to determine the success rate after the removal of the tumour. An insulin test may be used along with blood glucose and glycated haemoglobin (HbA1c) tests to monitor type 1 diabetes mellitus.

Understanding the test results of the fasting insulin test

Always take a healthcare provider’s opinion while interpreting the results of the insulin test and do not self-diagnose. Usually, the insulin and glucose tests are ordered together and interpreted accordingly.

Generally, a high level of insulin can indicate type 2 diabetes mellitus, hypoglycemia (low blood sugar), insulin resistance, Cushing’s syndrome, and pancreatic tumour. Low levels of insulin may be associated with type 1 diabetes mellitus, hyperglycemia (high blood sugar), and inflammation of the pancreas. 

The normal levels of insulin in the body are as follows :

  • after nearly eight hours of fasting is less than 25 mIU/L,
  • 30 minutes after glucose administration is 30-230 mIU/L, 
  • one hour after glucose ingestion is 18-276 mIU/L
  • two hours after glucose ingestion is 16-166 mIU/L, and
  • three hours or more after glucose ingestion is less than 25 mIU/L.

 In a healthy person, the insulin level is in proportion with the glucose level.

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Frequently Asked Questions:

Why do I need a Fasting Insulin Test?

Insulin tests are usually advised when a person is experiencing symptoms of low blood sugar such as trembling, sweating, confusion, irregular heartbeats, blurred vision, dizziness, and extreme hunger. Additionally, it is also advised if the blood glucose test reports low blood sugar levels.

What happens during the Fasting Insulin serum Test?

The blood samples are taken by the healthcare professional via a small needle prick from the veins on the inside of the patient's elbow. A small amount of blood is collected into a vial or test tube after the needle is inserted. A slight stinging sensation can be expected during the needle insertion and removal. The insulin test results are available within the same day.

What does an insulin test show?

The insulin test will show whether the insulin production is normal, the cause of low blood sugar, the need for insulin supplementation, and the presence of insulinoma.

What does a high insulin blood test mean?

High insulin level is termed hyperinsulinemia and is associated with an overworked pancreas, and eventually can result in diabetes mellitus. A high insulin level, together with a slightly high or normal glucose level, indicates insulin resistance in the body. After fasting, high insulin levels, followed by a glucose level less than 40mg/dL, and high levels of C-peptide and proinsulin indicate the presence of insulinoma. Rare cases of hyperinsulinemia are also associated with excessive growth of insulin-producing cells in the pancreas. Insulin levels are either normal or high in the primary stages of type 2 diabetes mellitus.

What happens when you have high insulin levels?

The symptoms of high insulin levels may not be very noticeable at times. The symptoms include excessive and frequent hunger and thirst, low blood sugar, weight gain, sweet cravings, difficulty focusing, tiredness, and anxiety.

What is an insulin blood test called?

The insulin blood test is also called fasting insulin, insulin serum, and total and free insulin tests.

What causes low insulin levels?

Low insulin levels or hypoinsulinemia are associated with obesity, hypothyroidism, a diet high in carbohydrates, and a sedentary lifestyle. At times, the cells become more resistant to insulin leading to an increase in both insulin and glucose levels. Eventually, the pancreas gets damaged, resulting in a decreased synthesis of insulin and causing hypoinsulinemia.

How to check Fasting insulin levels?

To check fasting insulin levels, consult a healthcare provider, fast for 8-12 hours, and have a blood sample taken. The sample is then analyzed in a lab to measure insulin levels. Elevated levels may indicate insulin resistance or other conditions. Discuss the results with your provider for further evaluation and guidance.
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