This test is principally used in the evaluation of hypoglycemia. Individuals with insulin-secreting tumors have high levels of both C-peptide and endogenous insulin. Individuals with factitious hypoglycemia will have low C-peptide levels in the presence of elevated serum insulin. C-peptide is also useful in assessing residual beta cell function in insulin-dependent diabetics, who may have antibodies that interfere with insulin assays. Further research has demonstrated glucagon-stimulated C-peptide concentration to be a good discriminator between insulin-requiring and noninsulin-requiring diabetic individuals. The identification of islet cell tumor is supported by elevation of C-peptide.
Should be fasting for 14-16 hours for basal values