Also known as:
Name:
Related tests: C-peptide, Glucose
Why is the test done?
To assess insulin production, to diagnose insulinoma (an insulin-producing tumour) and to investigate the causes of hypoglycaemia.
When is it done?
When there is hypoglycaemia.
When there are symptoms suggesting inappropriate insulin production. To monitor insulin production in people with diabetes.
What samples are required?
A blood sample taken from a vein or, in newborn babies, by heel-prick.
What is being tested?
Insulin is a hormone produced and stored in the beta cells of the pancreas. It regulates blood glucose and the metabolism of carbohydrates and stored fats.
After a meal, when blood glucose rises, insulin promotes the uptake of glucose by cells, particularly muscle and fat cells, which use it as a source of energy. Insulin also stimulates the liver to store excess glucose as carbohydrate (glycogen) or fatty acids.
Insulin is essential for human survival. Without insulin, glucose cannot enter cells and blood glucose levels rise until diabetic coma, a life-threatening condition, develops.
In type 1 diabetes the body’s own insulin production is so low that insulin must be given several times a day.
In type 2 diabetes insulin is produced, but medicines are needed that increase the cells’ response to insulin (over time or with obesity, cells can become resistant) or that stimulate insulin production. In some cases of type 2 diabetes, insulin injections may be needed to reach normal blood glucose levels.
Blood insulin and glucose must be in balance. Hyperinsulinaemia, an excess of insulin caused by an insulinoma (an insulin-producing tumour) or by giving too much insulin, can be dangerous. It causes hypoglycaemia, with sweating, a rapid heartbeat, hunger, confusion, visual disturbances and fainting. Since glucose is the brain’s main source of energy, the lack of glucose due to hyperinsulinaemia can fairly quickly lead to insulin shock and death.
How is it used?
When is it requested?
What does the test result mean?
Is there anything else I should know?
How is it used?
Blood insulin is often used together with blood glucose and C-peptide to diagnose insulinoma and to find the cause of hypoglycaemia. Insulin and C-peptide can be used to monitor the insulin the body produces itself (endogenous insulin), to detect an inappropriate response to insulin (insulin resistance) and to decide when to add insulin to oral diabetes medicines in the treatment of type 2 diabetes.
Insulin is sometimes measured together with the glucose tolerance test (GTT). Blood glucose and sometimes insulin are measured to assess insulin resistance, particularly in obese people.
When is it requested?
Insulin is often requested after abnormal blood glucose values are found and/or when there are acute or chronic symptoms of hypoglycaemia such as sweating, palpitations, hunger, confusion, visual disturbances and fainting (although these symptoms can have other causes).
Insulin and C-peptide are produced in equal amounts. Both may be requested to assess how much insulin is produced by the body and how much comes from outside (injected). Insulin measurement reflects the total amount, while C-peptide reflects only the body’s own production. Both may be requested to check that an insulinoma has been completely removed or to monitor insulin production after a pancreatic islet cell transplant.
What does the test result mean?
Insulin concentrations must be assessed in the clinical context. If fasting insulin and glucose concentrations are normal, the blood glucose control system is very probably working properly. If insulin levels are raised and glucose is normal or moderately raised, there may be insulin resistance. If insulin is low and glucose high, there is probably insufficient insulin production. If insulin is normal and glucose low, the hypoglycaemia is due to excess insulin.
Raised insulin concentrations are found in the following conditions:
1. Acromegaly
2. Cushing’s syndrome
3. Medicines such as corticosteroids, levodopa and oral contraceptives
4. Fructose or galactose intolerance
5. Insulinoma
6. Obesity
7. Insulin resistance, which occurs in type 2 diabetes
Reduced insulin concentrations are found in:
1. Diabetes
2. Hypopituitarism
Is there anything else I should know?
Injected insulin used to be of animal origin (produced from cattle or pig pancreatic cells). Today most insulin is synthetic and fully comparable to human insulin.
There are different preparations with different properties. Some are rapid-acting insulins with a short duration of action, and others are slow- and ultra-slow-release preparations. A person with diabetes may take different types of preparation during the day.
Insulin results may differ depending on the method used. The various methods differ in their ability to recognise different types of insulin. If the result does not match what is expected, the laboratory should be told what type of insulin is being given. Periodic insulin measurements should always be carried out in the same laboratory to ensure a consistent method.
If anti-insulin antibodies are present, they can interfere with the test, and they may need to be removed to ensure an accurate measurement of insulin concentration.
If anti-insulin antibodies are present, they may be measured whenever insulin is measured and when a change in the type of insulin given is being considered.
1. Can insulin be measured at home?
2. Why does insulin have to be injected?
3. How is an insulinoma treated?
4. What is insulin resistance?
1. Can insulin be measured at home?
No. Unlike glucose, insulin measurement requires suitable equipment and training.
2. Why does insulin have to be injected?
It cannot be taken by mouth because the insulin would be digested in the stomach.
3. How is an insulinoma treated?
Insulinomas are insulin-producing tumours and are often not malignant. They are removed surgically and, once removed, generally do not come back.
4. What is insulin resistance?
It is a reduced ability of insulin to help glucose enter cells, where it is needed to produce energy. The pancreas tries to compensate by producing more insulin. This results in high concentrations of insulin and C-peptide and normal or high glucose. Glucose, insulin and C-peptide concentrations can help identify this condition.
Insulin resistance is a warning sign of impaired glucose metabolism and of the risk of developing diabetes. Early or moderate insulin resistance often causes no symptoms, but if ignored it increases the risk of developing type 2 diabetes, high blood pressure, high blood lipids and/or heart disease over the years. (These four conditions make up what is sometimes called insulin resistance syndrome.)
Risk factors for insulin resistance include:
• Obesity, especially abdominal obesity
• Family history of diabetes
• Gestational diabetes
• Polycystic ovary syndrome
Treatment of insulin resistance involves changes in diet and lifestyle, such as losing excess weight, taking regular moderate exercise and increasing dietary fibre, to lower insulin levels and increase insulin sensitivity.