From the Guidelines
A C-peptide test is only indicated in people receiving insulin treatment, and it should be measured prior to insulin discontinuation to exclude severe insulin deficiency, as stated in the most recent guidelines 1.
C-Peptide Test Overview
The C-peptide test measures the amount of C-peptide in the blood, which indicates how much insulin the pancreas is producing. This test is primarily used to help distinguish between type 1 and type 2 diabetes, evaluate insulin production, and investigate causes of hypoglycemia.
Key Points to Consider
- Normal C-peptide levels typically range from 0.5 to 2.0 ng/mL, but these values can vary between laboratories.
- Low C-peptide levels suggest type 1 diabetes or insulin deficiency, while normal or high levels typically indicate type 2 diabetes or insulin resistance.
- The test requires a blood sample, usually taken after fasting for 8-12 hours, though sometimes it's performed after a meal or as part of a glucose tolerance test.
- C-peptide is produced in equal amounts to insulin when proinsulin splits into insulin and C-peptide, making it a reliable marker of natural insulin production.
- Unlike measuring insulin directly, C-peptide testing isn't affected by injected insulin, providing a more accurate assessment of the body's own insulin production capacity in patients already receiving insulin therapy.
Clinical Guidelines
According to the latest guidelines from the Diabetes Care journal 1, a C-peptide test is only indicated in people receiving insulin treatment, and it should be measured prior to insulin discontinuation to exclude severe insulin deficiency. The guidelines also recommend that C-peptide testing should not be performed within 2 weeks of a hyperglycemic emergency.
Conclusion Not Applicable
Instead, the key takeaways are:
- C-peptide testing is a valuable tool in the diagnosis and management of diabetes.
- It should be used judiciously, following the latest clinical guidelines 1.
- The test results should be interpreted in the context of the patient's clinical presentation and medical history.
From the Research
C-Peptide Test Overview
- The C-peptide test is used to measure the level of C-peptide in the blood, which reflects the functional β-cell mass and endogenous insulin secretion in patients with diabetes 2, 3.
- C-peptide is co-secreted with insulin and is not subject to hepatic clearance, making it a reliable marker of pancreatic beta cell function 2, 4.
Clinical Utility of C-Peptide Measurement
- The measurement of C-peptide can be helpful in clinical practice, particularly in distinguishing type 2 diabetes from Latent Autoimmune Diabetes in Adults and late-onset type 1 diabetes 2, 3.
- C-peptide levels can identify individuals at risk for or with type 1 diabetes with residual β-cell function, and can aid in evaluating β cell-sparing interventions 2, 5.
- The key current clinical role of C-peptide is to assist classification and management of insulin-treated patients, with utility greatest after 3-5 years from diagnosis 3.
Methods of C-Peptide Testing
- Methods of estimation include urinary and unstimulated and stimulated serum sampling, with modern assays detecting levels of C-peptide that can be used to guide diabetes diagnosis and management 4.
- The glucagon stimulation C-peptide testing is recommended due to its balance of sensitivity and practicality 4.
- A mixed meal tolerance test is considered the gold standard of measuring beta cell function in type 1 diabetes, but the method is laborious and inconvenient 5.
Interpretation of C-Peptide Results
- A C-peptide level of less than 0.2 nmol/l is associated with a diagnosis of type 1 diabetes mellitus (T1DM) 4.
- C-peptide levels are associated with diabetes type and duration of disease, and may correlate with microvascular and macrovascular complications and future use of insulin therapy 4, 6.
- The measurement of C-peptide can inform clinicians about probable pathophysiology and disease progression, enabling personalization of management and therapy 6.