• Credits

  • Section Writer: Dr. Om J Lakhani
  • Section Editor: Dr. Om J Lakhani

• Q. What is C-peptide ?

  • The pancreatic proinsulin is broken down into insulin and C-peptide
  • The C-peptide is released in equimolar concentration as insulin

• Q. What are the various ways in which C-peptide is measured ?

  • C peptide measurement in blood
    • Fasting
    • Stimulated
    • Random C peptide
  • Urine C peptide can also be measured – requires 24 hr collection

• Q. Of the above, which is a good marker of Beta-cell reserve ?

  • Stimulated C peptide is a marker of Beta cell reserve

• Q. What are the methods for "stimulation" in C-peptide ?

  • Glucose load
  • Mixed meal
  • Glucagon

• Q. Broadly, what is the difference between C-peptide in type 1 and type 2 diabetes in terms of stimulation test ?

  • Type 1 there is little or no increase in C peptide over baseline
  • Type 2 there is some increase in C peptide over baseline

• Q. What basal c-peptide value helps discriminate type 1 from type 2 diabetes ?

  • About 80% of Basal C-peptide levels below a cutoff of 0.6 ng/ml (0.2 nmol/l) have type 1 diabetes
  • Similarly 80% of patients with stimulated C-peptide <1 nmol/l have type 1 diabetes

• Q. Is Random C-peptide useful ?

  • One study showed that random C peptide was better than fasting and stimulated C peptide for classification of diabetes mellitus

• Q. What is the interpretation of non-fasting Random c-peptide value ?

• <0.6 ng/ml - Strongly suggestive of absolute insulin deficiency and type 1 diabetes

• <1.8 ng/ml- Unlikely to achieve glycemic control without the use of Multiple insulin doses

• More than 3 ng/ml- Unlikely to be type 1 diabetes- more likely to be Type 2 or MODY

• Q. Describe the protocol for Glucagon stimulated C-peptide

  • Draw baseline fasting specimen. (12 hour of overnight fast)
  • Administer 1 mg Glucagon I.V.
  • Draw additional specimens at 6 and 10 minutes post-glucagon

• Q. What is the protocol for mixed-meal stimulation test ?

  • 1. Fasting - Measure FBS and C-peptide
  • 2. Give liquid mixed meal - Sustacal or Ensure Plus powder - 6 scoops in 200 ml water
  • 3. Measure RBS and C-peptide 90 min after liquid meals

• Q. What is Sustacal ?

  • It is basically a protein supplement from Nestle
  • ENSURE PLUS powder can be used as a substitute which has similar composition
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• Q. In terms of percentage what is the percentage of C-peptide elevation post-baseline

  • Normal stimulation of c-peptide is a 150-300% elevation over basal levels.

• Q. Give the scoring of C-peptide post mixed meal stimulation used by Department of Endocrinology at Zydus hospital ? (Unpublished)

  • 

  • Total score

    • ≥5 - stongly suggestive of Type 1 diabetes
    • 3-5- Suggestive of type 1
    • 0-3- Unlikely to be type 1 but close follow-up is required
    • 0 - not type 1

• Q. In a patient with type 2 diabetes, what value of C-peptide suggest the need for basal-bolus insulin (Multiple dose insulin) for diabetes management as compared to basal insulin with OAD ?

  • Post-stimulation C-peptide <3.1 ng/ml - suggestive of need for MDI therapy instead of basal only

• Q. What cut-off is suggestive of Insulin mediated hypoglycemia in patients undergoing 72 hour fast test for hypoglycemia evaluation ?

  • When glucose value is <55 mg/dl- C-peptide value of >0.6 ng/ml is strongly suggestive insulin mediated hypoglycemia

#Updates

• Source: Talk on "Practical use of C-peptide in clinical practice"

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