Lab Test: C Peptide, Insulin C Peptide (Blood) Level
- Measurement of C-peptide in blood for the evaluation and treatment of disorders related to abnormal insulin levels, such as diabetes, hypoglycemia, and insulinoma.
- Used to identify patients who secretly self-administer insulin.
- Adults: 0.5-2.0 ng/mL (0.17-0.66 nmol/L)* (PDr)
- Fasting: 0.78-1.89 ng/mL or 0.26-0.62 nmol/L (SI units)
- 1 hour after glucose load: 5-12 ng/mL
- Determination of etiology of acute or recurrent hypoglycemia - decreased C-peptide levels of 2 ng/mL or less associated with high insulin levels in patients experiencing hypoglycemia suggest exogenous (factitious) hyperinsulinism. Decreased C-peptide with low insulin and low glucose levels is associated with non-insulin-mediated hypoglycemias from liver disease, ethanol hypoglycemia, or adrenal insufficiency. Increased C-peptide levels > 2 ng/mL, with elevated insulin and proinsulin levels, are usually seen in patients with insulinomas or hypoglycemia secondary to oral hypoglycemic (e.g., sulfonylureas) use.
- Patients with reactive (alimentary) hypoglycemia often present with high insulin levels; the insulin to C-peptide molar ratio will be disproportionately high.
- Distinguishes type 1 from type 2 diabetes mellitus - Decreased C-peptide and insulin levels associated with islet cell antibodies suggest type 1 diabetes.
- Elevated C-[e[tide and insulin levels without autoimmune markers suggest type 2 diabetes.
- Suspected insulinoma - Increased C-[e[tide, insulin, and proinsulin levels with low beta hydroxybutyrate serum concentrations is suggestive of insulinoma. C-peptide levels of 2 nmol/L or greater usually indicate insulinoma. The diagnosis of insulinoma is usually made during a prolonged fast using the clinical findings of Whipple's triad: symptomatic patients with serum glucose levels less than 45 mg/dL, symptoms of hypoglycemia while fasting, and relief of symptoms following administration of glucose.
- Pancreas transplant
- Renal failure
- Administration of oral hypoglycemic agents
- Factitious hypoglycemia
- Diabetes mellitus
- Total pancreatectomy
- Glucose, Blood.
- Glucagon - an islet cell hormone that acts to increase serum glucose levels.
- Glycosylated hemoglobin - an indirect measure of the chronic state of glucose levels.
- Insulin assay - direct measurement of insulin.
- Renal failure can cause increased levels of C-peptide.
- Drugs that may cause increased levels of C-peptide include oral hypoglycemic agents (e.g., sulfonylureas).
- Collect a venous blood sample.
- Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding.
- Explain the procedure to the patient.
- Instruct the patient to fast for 8 to 10 hours before the test. Only water is permitted.
C-peptide is a protein that connects the beta and alpha chains of proinsulin. In the beta cells of the islet of Langerhans of the pancreas, the chains of pros=insulin are separated during the conversion of proinsulin to insulin and C-peptide. C-peptide is released into the portal vein in nearly equal amounts. The capacity of the pancreatic beta cells to secrete insulin can be evaluated by directly measuring either insulin or C-peptide. In some instances, C-peptide levels more accurately reflect islet cell function.
Increased levels indicate:
Decreased levels indicate:
MESH Terms & Keywords