From the Guidelines
Fasting C-peptide levels are primarily used to distinguish between type 1 and type 2 diabetes, particularly in ambiguous cases, and to assess pancreatic beta cell function 1. When interpreting fasting C-peptide levels, it is essential to consider the clinical context and the presence of hyperglycemia.
- Low C-peptide levels indicate decreased insulin production, suggesting type 1 diabetes.
- Normal or elevated levels in the presence of hyperglycemia suggest insulin resistance as seen in type 2 diabetes. The measurement of C-peptide can aid in differentiating between type 1 and type 2 diabetes, especially when the clinical presentation is unclear 1. Additionally, fasting C-peptide levels can be useful in diagnosing insulinomas and investigating suspected factitious hypoglycemia, as they are not affected by exogenous insulin administration 1. It is recommended to measure fasting C-peptide level when simultaneous fasting plasma glucose is £220 mg/dL (12.5 mmol/L), particularly if required by the payer for coverage of insulin pump therapy 1. Overall, fasting C-peptide testing provides valuable information for determining appropriate diabetes treatment strategies and assessing pancreatic function.
From the Research
Use of Fasting C-peptide Levels
- Fasting C-peptide levels are used to measure endogenous insulin secretion in patients with diabetes 2, 3, 4, 5, 6
- C-peptide is produced in equal amounts to insulin and is a reliable indicator of pancreatic beta-cell function 2, 4, 5
- Measurement of fasting C-peptide levels can help differentiate between type 1 and type 2 diabetes 2, 3, 4, 6
- Fasting C-peptide levels can also be used to predict the need for insulin therapy in patients with type 2 diabetes, although its ability to do so is limited 3
- A low fasting C-peptide level can indicate absolute insulin deficiency and the need for insulin treatment, while a high level may suggest insulin resistance 4, 5
Clinical Applications
- Fasting C-peptide levels can be used to assist in the diagnosis and classification of diabetes, including latent autoimmune diabetes in adults (LADA) and maturity-onset diabetes of the young (MODY) 4
- C-peptide measurement can help identify patients with type 1 diabetes who are likely to experience partial remission during the first year of treatment 4
- Fasting C-peptide levels can also be used to monitor the effectiveness of treatments aimed at preserving insulin secretion, such as islet cell transplantation 4, 5