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Insulin Blood Test

Last updated March 27, 2018

Insulin is a protein molecule that is manufactured by beta cells in the islets of Langerhans, in the pancreas. Insulin is made from proinsulin, which consists of two chains, mainly A-chain and B-chain that are linked to each other with C-peptide.


What are the other Names for this Test? (Equivalent Terms)

  • Insulin Test
  • Serum Insulin Level
  • Total and Free Insulin (Blood)

What is Insulin Blood Test? (Background Information)

  • Insulin is a protein molecule that is manufactured by beta cells in the islets of Langerhans, in the pancreas
  • Insulin is made from proinsulin, which consists of two chains, mainly A-chain and B-chain that are linked to each other with C-peptide. The A-chain, B-chain, and C-peptide, are together called proinsulin. The insulin molecule is made, after removing the C-peptide
  • Increased levels of proinsulin are normally found in infants and preterm neonates. Increased levels of pro-insulin are present in type II diabetes and also in pre-type I diabetes
  • Markedly elevated levels of pro-insulin are found in familial hyper-proinsulinemia which is a genetic condition that results in mutations from proinsulin gene. This condition can be found in individuals of Japanese heritage
  • Increased levels of insulin can be noted in cirrhosis of liver

The testing for insulin level should be performed along with glucose level. Insulin is a hormone that helps transport glucose from blood into the tissue. Glucose is necessary for energy functions of the cells. Decreased glucose within the cells will lead to starvation of the cells.

In type I diabetes, generally the insulin levels are decreased, which results in increased glucose level in blood and decreased transport of glucose into the cells. In type II diabetes, there is an insulin resistance, which leads to decreased transport from the blood into the tissues. Individuals with insulin resistance would have high levels of insulin, in their blood.

What are the Clinical Indications for performing the Insulin Blood Test?

  • In clinical situations where there is increase in insulin levels, it would result in hypoglycemia. Such marked increase in insulin levels can be found in insulin-secreting tumors called insulinomas
  • Individuals with insulinomas have low glucose levels, resulting in hypoglycemic symptoms, such as excessive sweating, faint-headedness, palpitations, hand tremors and mental confusion
  • It is important to do a C-peptide level test long with Insulin Level Test to determine the cause of hypoglycemia
  • Individuals with insulinomas have high insulin level and C-peptide level
  • On the contrary, hypoglycemia that is caused from an injected or exogenous insulin source is characterized by low C-peptide levels and high insulin levels
  • In individuals diagnosed with type I diabetes, low C-peptide levels occur due to a decrease in insulin production

The Insulin Blood Test is usually ordered jointly with glucose levels and C-peptide levels tests. They are usually ordered when an individual has hypoglycemic (very low blood sugar) symptoms, such as:

  • Palpitations
  • Mental confusion
  • Fainting
  • Increased sweating
  • Nervousness
  • Hypoglycemic seizure

Both the insulin and C-peptide levels (tests) are also performed together to determine, whether the insulin is due to an endogenous source (produced within the body) or from an exogenous source (injected by an external source).

How is the Specimen Collected for Insulin Blood Test?

Specimen required: Blood

Process: The blood sample is collected using a syringe inserted into a superficial vein of the arm.

Preparation required: Generally an 8-hour fasting is necessary, before the blood sample is collected.

What is the Significance of the Insulin Blood Test Result?

Significance of an Insulin Blood Test:

  • In a normal, healthy individual, both the fasting insulin levels and the fasting glucose levels are normal
  • In individuals with type II diabetes, who show insulin resistance, there is an increased level of fasting insulin and glucose
  • In type I diabetes, where there is a decreased insulin production, the fasting insulin level is low and the fasting blood glucose level high
  • With insulin-producing tumors, such as insulinomas, the fasting insulin level is increased and the fasting glucose level is decreased. The pattern noted in insulinomas, can also be seen in exogenous administration of insulin, increased steroidal secretion within the body, such as due to Cushing syndrome and steroidal administration for a variety of clinical conditions
  • Increased insulin levels are noted in pituitary tumors causing increased growth hormone production, oral contraceptive use, and excessive body weight
  • Decreased insulin levels can be seen due to decreased function of the pituitary gland (hypopituitarism) and pancreatic conditions, leading to destruction of pancreatic gland, such as due to chronic pancreatitis and pancreatic tumors

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • The insulin levels in the serum can be falsely low due to hemolysis (breakdown of RBCs) of the blood specimen collected. The red blood cells contain an enzyme that destroys insulin. The hemolysis process results in release of the enzyme that destroys insulin resulting in falsely low insulin levels, when tested
  • Some individuals have insulin antibodies, which can affect the testing process of insulin levels. Such insulin antibodies can either, falsely increase or falsely decrease the insulin levels
  • Tests usually performed in conjunction with Insulin Blood Test, include glucose tolerance test, blood glucose levels, and C-peptide assay

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:


Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Aug. 21, 2013
Last updated: March 27, 2018

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