Description
Insulin may be used, often along with glucose and C-peptide levels, to help diagnose insulinomas and to help diagnose documented chronic (fasting) hypoglycemia. Insulin and C-peptide levels may also be used to monitor endogenous insulin, check for insulin resistance, and to help determine when a type 2 diabetic might need to start taking insulin injections to supplement oral medications.
Insulin levels are used in conjunction with the glucose tolerance test (GTT). In this situation, blood glucose and insulin levels are measured at pre-established time intervals to evaluate insulin resistance.
Its concentration is measured by means of analysis of a blood sample drawn from the vein in the arm.
Purpose of the test
Insulin levels are most frequently ordered following an abnormal glucose test and/or when a patient has acute or chronic symptoms of hypoglycemia, such as sweating, palpitations, hunger, confusion, blurred vision, dizziness, fainting, and seizures.
Insulin and C-peptide are produced by the body at similar rate as part of the activation and division of proinsulin in the pancreas. Both may be ordered to evaluate how much insulin in the blood is due to endogenous production and how much is from exogenous sources. Insulin tests will reflect the total, while C-peptide will reflect only the endogenous insulin.
Doctor may order both tests to verify that an insulinoma has been successfully removed.
Reference range values
3-19 mIU/L
Abnormal findings
High insulin levels are seen with:
- Acromegaly
- Cushing's syndrome
- Drugs such as corticosteroids, levodopa, oral contraceptives
- Fructose or galactose intolerance
- Insulinomas
- Obesity
- Insulin resistance, such as in type 2 diabetes and metabolic syndrome
Low insulin levels are seen with:
- Diabetes
- Hypopituitarism
- Pancreatic diseases such as chronic and pancreatic cancer