Peptide C measurement is used to investigate cases of hypoglycaemia as well as to assess insulin reserve in certain categories of diabetic patients who either have autoantibodies against insulin or receive insulin therapy.
Proinsulin is converted to insulin in the pancreatic beta cells. A by-product of this conversion is peptide C (C-Peptide, Connecting Peptide or Binding Peptide), an inactive 31 amino acid polypeptide chain. Peptide C levels are usually associated with endogenous insulin production and are not affected by exogenous (pharmaceutical) insulin administration. Measuring the levels of peptide C is useful:
- In the determination of endogenous insulin levels, as the concentration of peptide C is not affected by exogenous insulin administration
- Determining whether hypoglycaemia is caused by non-therapeutic insulin injections (plasma hypoglycaemia), in which case peptide C levels will be low while the insulin levels will be elevated
- In determining the presence of insulinoma, there may be elevated concentrations of both insulin and peptide C
- In monitoring for recurrence of insulinoma, indicated by elevated levels of peptide C
Peptide C levels are not always correlated with endogenously produced insulin in obese patients and in patients with islet cell pancreatic tumors. In addition, hepatic impairment can cause elevated levels of C peptide.
Possible Interpretations of Pathological Values
- Increase: Male obesity, cardiac arrhythmias (QT prolongation), islet cell cancer. Medications: Oral hypoglycaemic agents and sulfonylureas. High intake of fructose and high glycemic index foods are associated with higher levels of C peptide.
- Decrease: Diabetes mellitus, disorders of the pancreas in alcoholics. Medications: Rosiglitazone, Troglitazone.
Laboratory test results are the most important parameter for the diagnosis and monitoring of all pathological conditions. 70%-80% of diagnostic decisions are based on laboratory tests. Correct interpretation of laboratory results allows a doctor to distinguish "healthy" from "diseased".
Laboratory test results should not be interpreted from the numerical result of a single analysis. Test results should be interpreted in relation to each individual case and family history, clinical findings and the results of other laboratory tests and information. Your personal physician should explain the importance of your test results.
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