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What is an Insulin test?

Insulin is a vital hormone secreted by the beta cells of pancreas. It regulates glucose metabolism by assisting the transport of glucose from blood to tissue cells. Glucose is an important energy source in the body. Raised blood glucose levels after a meal stimulate beta cells to secrete insulin to transport excess sugar out of the bloodstream. Insulin thus plays an important role in regulating glucose levels inbody.

In certain disorders, beta cells cannot secrete enough insulin, causing an increased blood glucose state called hyperglycaemia. In other scenarios, insulin secretion in body may be normal, but body cells become resistant to its effects. This condition is known as ‘insulin resistance’. In Type 1 diabetes, also known as insulin-dependent diabetes mellitus, reduced insulin secretion is the cause of hyperglycaemia, whereas Type 2 diabetes mellitus usually results due to insulin resistance. Occasionally, increased levels of insulin are observed in the body due to hyperinsulinemia. It may lead to various metabolic imbalances.

An insulin test is a blood test used to detect the levels of insulin in blood. Insulin levels in blood may be indicative of the probable cause of metabolic derangements occurring in the body. 

  1. Why is an Insulin test performed?
  2. How do you prepare for an Insulin test?
  3. How is an Insulin test performed?
  4. Insulin test results and normal range

An insulin test is performed to evaluate patients with abnormal blood glucose levels, particularly in hypoglycaemia. The symptoms of hypoglycaemia include

An insulin test is also useful for people with insulin resistance. Insulin resistance can be seen in Type 2 diabetes mellitus, polycystic ovary syndrome, obesity, family or genetic history of insulin resistance or a history of heart disease or stroke.

An insulin test, along with the measurement of blood glucose, C-peptides and proinsulin is used to diagnose a disease called “insulinoma” (tumour secreting excessive amount of insulin). The patient is subjected to prolonged fasting for this test. Insulin test is also useful for monitoring the effectiveness of treatment after surgical removal of insulinoma tumour.

(Read more: Diabetes causes)

Fasting for 8 hours or more is needed to perform an insulin test; however, water is allowed. Detailed procedure and precautions should be explained to the patient prior to the test. If a patient is taking insulin injections or other medications, it should be withheld before this test, as they can affect the outcome of the test.

Insulin test is performed by collecting blood from a vein of arm in a fasting patient. A laboratory technician inserts a needle into the vein by a simple prick and collects about 5 to 7 mL of blood in a collection tube. More blood volume may be required if other tests are also performed with this test. Slight pain may be felt at the site of insertion of needle. The sample is then sent to the laboratory for analysis. The whole procedure usually requires a few minutes. If there are symptoms of pain or bleeding after the procedure from the site of needle prick, inform the doctor as soon as possible. Any medications that you have been taking can be resumed after blood collection under the guidance of a physician.

Normal results: Insulin values are measured in micro international units per millilitre (μIU/mL) or picomole per litre (pmol/L). The normal serum insulin levels are less than 17 μIU/mL.

Abnormal results: Increased levels of insulin are seen in the following diseases/conditions:

  • Hypoglycaemia (low blood glucose)
  • Type 2 diabetes mellitus
  • Acromegaly
  • Cushing’s syndrome
  • Intolerance to galactose or fructose sugars
  • Insulinoma (tumour secreting excessive insulin)
  • Insulin injection or insulin overdose
  • Insulin resistance
  • Obesity
  • Liver diseases
  • Lesions in pancreas
  • Hypoglycaemia caused by certain medications used for diabetes mellitus (sulfonylureas)

Decreased levels of insulin are seen in the following diseases/conditions:

  • Hyperglycaemia (high blood glucose)
  • Reduced pituitary gland function
  • Type 1 diabetes mellitus (untreated)

As discussed earlier, the insulin test is usually recommended with other blood tests, such as blood glucose test, C-peptide assay or oral glucose tolerance test. Hence, it is useful to discuss with the doctor about specific precautions to be followed for these tests. After the analyses of the test results, the doctor may advise other tests, such as radiological examination for the diagnosis and treatment of the exact underlying problem.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. This information is purely from an educational perspective and is in no way a substitute for medical advice from a qualified doctor. 

Lab Tests recommended for Insulin Test

Insulin ( PP ) - Insulin Post Prandial

25% छूट + 5% कैशबैक

Insulin Fasting

25% छूट + 5% कैशबैक


  1. Rudy Bilous, Richard Donnelly. Handbook of Diabetes. Normal physiology of insulin secretion and action. 4th Edition. 2010 pp 22-34.
  2. Ndisang JF, Vannacci A, Rastogi S. Insulin Resistance, Type 1 and Type 2 Diabetes, and Related Complications 2017. J Diabetes Res. 2017;2017:1478294
  3. American Diabetes Association [internet]; Hypoglycemia (Low Blood Glucose)
  4. National Institute of Diabetes and Digestive and Kidney Diseases [internet]: US Department of Health and Human Services; Low Blood Glucose (Hypoglycemia)
  5. National Institute of Diabetes and Digestive and Kidney Diseases [internet]: US Department of Health and Human Services; Insulin Resistance & Prediabetes
  6. Okabayashi T, Shima Y, Sumiyoshi T, et al. Diagnosis and management of insulinoma. World J Gastroenterol. 2013;19(6):829-837.
  7. Wilson DD. McGraw-Hill’s Manual of Laboratory & Diagnostic Tests. Insulin (Insulin Assay, Serum Insulin). 2008 pp 337-338.
  8. Fischbach FT. A Manual of Laboratory and Diagnostic Tests. Chapter on Diabetes Testing – Insulin. 7th Edition. 2003.
  9. Ferri FF. Ferri’s Best Test- A Practical Guide to Clinical Laboratory Medicine and Diagnostic Imaging. Insulin, free. 4th edition. 2019 pp 190.

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