From the Guidelines
C-peptide testing is a valuable tool for distinguishing between type 1 and type 2 diabetes, particularly in cases where the diagnosis is unclear, as stated in the most recent guidelines 1.
Key Points to Consider
- The test measures endogenous insulin production, which is essential for determining the type of diabetes and guiding treatment decisions.
- Normal C-peptide levels typically range from 0.5-2.0 ng/mL, with low levels indicating type 1 diabetes and normal to high levels suggesting type 2 diabetes.
- C-peptide testing is particularly useful when evaluating for insulin resistance or monitoring beta cell function over time.
- The test requires a blood sample and may be combined with glucose testing, with results interpreted in the context of other clinical information, such as kidney function, medications, and other factors.
- According to the latest guidelines, a C-peptide test is only indicated in people receiving insulin treatment, and a random sample with concurrent glucose can replace a formal C-peptide stimulation test in the context of classification 1.
Clinical Application
- C-peptide levels can help guide treatment selection, as patients with very low C-peptide may require insulin therapy, while those with adequate levels might respond to oral medications.
- In cases where the diagnosis is unclear, C-peptide testing can aid in differentiating between type 1 and type 2 diabetes, as recommended by the guidelines 1.
- Healthcare providers should consider C-peptide testing as part of a comprehensive diagnostic approach, taking into account clinical presentation, medical history, and other relevant factors.
- The latest guidelines emphasize the importance of careful monitoring and education for individuals with possible type 1 diabetes who are not treated with insulin, to rapidly initiate insulin therapy in the event of glycemic deterioration 1.
From the Research
C-peptide Measurement in Diabetes
- C-peptide is produced in equal amounts to insulin and is the best measure of endogenous insulin secretion in patients with diabetes 2, 3, 4, 5, 6
- Measurement of insulin secretion using C-peptide can be helpful in clinical practice, particularly in differentiating between type 1 and type 2 diabetes 2, 3, 4, 5, 6
Clinical Utility of C-peptide Measurement
- C-peptide measurement can assist in the classification and management of insulin-treated patients, with utility greatest after 3-5 years from diagnosis 2
- A low basal C-peptide level can be considered a criterion for transferring patients initially diagnosed with type 2 diabetes to the type 1 diabetes group 3
- C-peptide level may be a good predictor of clinical partial remission during the first year of type 1 diabetes 3
- C-peptide measurement can also be used to assist in patient selection for islet cell transplantation and post-transplant monitoring 3
Methods of C-peptide Estimation
- Methods of estimation include urinary and unstimulated and stimulated serum sampling 4
- Modern assays detect levels of C-peptide that can be used to guide diabetes diagnosis and management 4
- Glucagon stimulation C-peptide testing is recommended due to its balance of sensitivity and practicality 4
C-peptide Levels and Diabetes Type
- 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 level may correlate with microvascular and macrovascular complications and future use of insulin therapy, as well as likely response to other individual therapies 4
- C-peptide measurement can help reclassify diabetes types and provide more appropriate disease management 6
Limitations and Future Research
- The lack of robust evidence about the clinical utility of C-peptide measurement in type 2 diabetes limits its use in such cases 5
- Problems remain in the standardization of the assay for C-peptide, raising concerns about comparability of measurements between different laboratories 5
- Future research is needed to address current limitations and areas of uncertainties in the use of C-peptide measurement in diabetes management 5