From the Guidelines
C-peptide testing is typically ordered in diabetes to distinguish between type 1 and type 2 diabetes, assess beta cell function, and evaluate for insulin resistance, particularly in cases where the diagnosis is unclear or when considering insulin therapy in type 2 diabetes, as recommended by the most recent guidelines 1.
Key Indications for C-peptide Testing
- Distinguishing between type 1 and type 2 diabetes in adults with ambiguous presentation
- Suspected latent autoimmune diabetes in adults (LADA)
- Considering insulin therapy in type 2 diabetes
- Evaluating suspected factitious hypoglycemia or insulin overdose
Interpretation of C-peptide Levels
- Low C-peptide levels suggest type 1 diabetes or advanced type 2 diabetes with significant beta cell failure
- Normal or high levels typically indicate type 2 diabetes with insulin resistance
Clinical Utility
- C-peptide measurement can help monitor beta cell function over time in patients with type 2 diabetes to guide treatment decisions regarding insulin initiation
- It is an excellent marker of endogenous insulin production, as it is produced in equal amounts to insulin when proinsulin is cleaved
Recent Guidelines
- The 2024 guidelines for the diagnosis and classification of diabetes recommend C-peptide measurements to help distinguish type 1 from type 2 diabetes in ambiguous cases 1
- The guidelines also suggest that C-peptide testing 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
From the Research
C-Peptide Testing in Diabetes
- C-peptide is a measure of pancreatic beta cell function and is produced in equimolar amounts to endogenous insulin 2.
- It is used to guide diabetes diagnosis and management, with levels associated with diabetes type and duration of disease 2.
- A c-peptide level of less than 0.2 nmol/l is associated with a diagnosis of type 1 diabetes mellitus (T1DM) 2.
Clinical Utility of C-Peptide Measurement
- C-peptide measurement has a potential role in type 2 diabetes management, with levels correlating with microvascular and macrovascular complications and future use of insulin therapy 3, 4.
- Assessing C-peptide in patients with insulin-treated type 2 diabetes can help evaluate residual β-cell function and guide treatment decisions 4.
- C-peptide levels can predict the adoption of a basal-bolus treatment in insulin-treated patients with type 2 diabetes 4.
Limitations and Areas of Uncertainty
- 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.
- Further research is needed to clarify the value of C-peptide testing in understanding and managing type 2 diabetes and to highlight areas where further research is needed 3, 5.