C-Peptide

Casandra

Casandra Test Code LC61063Version 1 (DRAFT)

Performing Lab

Lab LabcorpLab Test ID 010108CPT Code 84681

Also known as: Connecting Peptide, Insulin C-Peptide, Proinsulin C-Peptide

Clinical Use

Order Test

Use

The principal use of C-peptide is in the evaluation of hypoglycemia. Patients with insulin-secreting neoplasms have high levels of both C-peptide and endogenous insulin; in contrast, patients with factitious hypoglycemia will have low C-peptide levels in the presence of elevated (exogenous) serum insulin. C-peptide is also useful in evaluating residual beta-cell function in insulin-dependent diabetics, many of whom have antibodies that interfere with insulin assays. Glucagon-stimulated C-peptide concentration has been shown to be a good discriminator between insulin-requiring and non−insulin-requiring diabetic patients. The diagnosis of islet cell tumor is supported by elevation of C-peptide when plasma glucose is low.

Special Instructions

Values obtained with different assay methods should not be used interchangeably in serial testing. Consistency in assay method is recommended for therapy monitoring. The procedure does not support serial monitoring; for such requirements, order the serial monitoring number 480108. Patients taking high doses of biotin supplements should stop 72 hours prior to sample collection, as they might interfere with test results.

Limitations

C-peptide levels can be elevated in renal failure since C-peptide is excreted by the kidneys. Cases exist where insulinoma presents with increased proinsulin but normal insulin and C-peptide levels. The test may yield erroneous results if the patient has been treated with monoclonal mouse antibodies or high titers of antibodies to streptavidin and ruthenium. Certain additives in the test aim to minimize these effects.

Test Details