The results of your C-peptide test will help your healthcare provider determine how much natural baseline insulin your body makes.
C-peptide results are reported with a reference range, which will vary from one lab to another. Your C-peptide may be high, low, or normal. In new patients, high levels tend to indicate type 2 diabetes, and low levels tend to indicate type 1 diabetes.
Nevertheless, this measurement can be difficult to interpret, and any result should be discussed with the healthcare professional who ordered your test and will help interpret it in the context of your blood sugar level.
High C-Peptide Levels
New patients with type 2 diabetes typically have C-peptide measurements on the high end of normal, or above the normal range. That’s because the insulin resistance characteristic of type 2 diabetes forces the pancreas to work harder and produce extra insulin.
Type 2 diabetes, however, is a progressive disease. Insulin resistance increases over time, and eventually, the overworked pancreas begins to lose its ability to produce insulin. The longer you have had type 2 diabetes, the more your C-peptide levels are likely to decline. After years or decades of life with type 2 diabetes, C-peptide may eventually be so low as to be undetectable.
A high C-peptide measurement may also indicate conditions other than diabetes, such as:
Low C-Peptide Levels
New patients with type 1 diabetes typically have C-peptide levels that are on the low end of normal, or below the normal range, indicating too little insulin secretion. People who develop type 1 diabetes as adults typically have a slower disease onset, and usually have more capacity to secrete insulin both when they are diagnosed and in the following years. In cases of severe onset, such as people diagnosed with diabetic ketoacidosis, there may be no evidence of C-peptide at all.
A C-peptide measurement, however, should not be used alone to diagnose type 1 diabetes. The official diagnostic criteria require both high blood sugar levels and the presence of the autoimmune markers that cause type 1 diabetes.
For people with longstanding type 1 diabetes, even very small amounts of measurable C-peptide are a good sign, and are associated with better blood sugar control, lower insulin requirements, and a lower risk of hypoglycemia.
A low C-peptide measurement can also indicate the presence of Addison’s disease or liver disease.
