C-Peptide PP
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C-Peptide is an indirect marker of insulin production by the pancreas
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🧪 C-Peptide – Postprandial (PP)
Test Name | C-Peptide (Postprandial) |
|---|---|
Sample Type | Serum (blood) |
Fasting Required | ✅ Eat a standard meal, and test is done 2 hours after |
Timing | Typically 2 hours after a meal or 75g glucose load |
Normal Range (PP) | ~1.5 – 7.0 ng/mL (varies slightly by lab and individual) |
Reporting Time | 1–2 working days |
Department | Endocrinology / Diabetology |
🧬 What is C-Peptide?
C-Peptide (Connecting Peptide) is a by-product of insulin production. It is formed when proinsulin splits into:
- Insulin (active hormone)
- C-Peptide (inactive peptide, serves as a marker of insulin secretion)
Because it is secreted in equal amounts with insulin, C-peptide reflects how much insulin your pancreas is making.
🧭 Why is the Postprandial Test Done?
The PP C-Peptide is especially useful to assess how your pancreas responds to a glucose challenge, such as:
- A meal (physiological)
- A glucose drink (oral glucose tolerance test)
It provides more dynamic information than fasting C-peptide, especially in borderline or early diabetes cases.
⚕️ Indications for Testing
Purpose | Use |
|---|---|
Assess beta-cell function | Especially in Type 2 or latent autoimmune diabetes (LADA) |
Distinguish between Type 1 & Type 2 diabetes | Type 1 = low C-peptide; Type 2 = normal/high postprandial levels |
Monitor insulin secretory capacity | Evaluate whether patient is insulin-dependent or not |
Evaluate hypoglycemia causes | Detect insulinoma, insulin overuse, or surreptitious insulin injections |
Pre- or post-pancreatic surgery | Assess residual pancreatic activity |
🔍 Interpretation of Results
C-Peptide Level (Postprandial) | Possible Meaning |
|---|---|
🔻 Low | - Type 1 diabetes |
✅ Normal to High | - Healthy pancreas |
🔺 Very High | - Insulinoma |
🔄 Tests Usually Done Alongside
Test | Purpose |
|---|---|
Fasting C-Peptide | Compare baseline vs meal response |
Blood Glucose (PP) | Evaluate insulin-glucose dynamics |
HbA1c | Assess long-term glycemic control |
Fasting Insulin | Calculate HOMA-IR for insulin resistance |
Anti-GAD / ICA Antibodies | Distinguish autoimmune diabetes (LADA or Type 1) |
💡 Fasting vs Postprandial C-Peptide
Aspect | Fasting C-Peptide | Postprandial C-Peptide |
|---|---|---|
When Measured | After 8–10 hours fasting | 2 hours after meal or glucose load |
Use Case | Baseline beta-cell function | Stimulated insulin response |
Better For | Diagnosing severe insulin deficiency | Borderline/early diabetes evaluation |
📋 Summary
Purpose | Assess post-meal insulin secretion by pancreas |
|---|---|
Useful For | Differentiating diabetes types, insulinoma, insulin reserve |
Sample Timing | 2 hours after eating or 75g glucose |
Paired With | Glucose, HbA1c, Fasting Insulin, Autoantibodies |
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