C-Peptide Assay (Fasting & Stimulated)
Fasting And Stimulated
Understanding how much insulin your body produces is a critical step in diagnosing and managing diabetes effectively. The C-peptide assay—conducted in both fasting and stimulated states—is one of the most reliable tests to measure your pancreas’s insulin-producing ability. It helps differentiate between Type 1 and Type 2 diabetes, detect latent autoimmune diabetes in adults (LADA), and assess beta-cell function, ultimately guiding your treatment plan.
What Is C-Peptide and Why Does It Matter?
C-peptide is a protein fragment released when proinsulin (the precursor of insulin) is split into insulin and C-peptide. While insulin acts quickly and is used by the body, C-peptide remains longer in the bloodstream, making it a more stable marker for assessing how much insulin your pancreas is producing naturally.
Types of C-Peptide Tests: Fasting vs Stimulated
- Fasting C-Peptide Test
This test measures basal insulin secretion—the amount of insulin your pancreas produces without any food stimulus.
- Preparation: 8–10 hours of fasting
- Purpose: To evaluate natural insulin production uninfluenced by meals
- Useful For:
- Diagnosing Type 1 diabetes (very low or absent C-peptide)
- Identifying insulin resistance in Type 2 diabetes (normal or high C-peptide)
- Monitoring insulin production in long-standing diabetes
- Stimulated C-Peptide Test
This test measures insulin response after food or glucose intake, reflecting post-meal pancreatic function.
- Procedure: A glucose drink or standard meal is given, and blood is drawn 90 minutes later
- Purpose: To observe insulin secretion in real-life conditions
- Useful For:
- Differentiating Type 1, Type 2, and LADA
- Evaluating whether insulin therapy is still required
- Assessing residual beta-cell function
- Supporting advanced treatment decisions (e.g. GLP-1 agonists vs insulin)
C-Peptide Reference Ranges
| Test | C-Peptide Level | Interpretation |
|---|---|---|
| Fasting | 0.5 – 2.0 ng/mL | Normal insulin production |
| < 0.5 ng/mL | Suggests low insulin (Type 1 diabetes) | |
| > 2.0 ng/mL | May indicate insulin resistance (Type 2 diabetes) | |
| Stimulated | 1.5 – 5.0 ng/mL | Normal post-meal insulin response |
| < 1.5 ng/mL | Low insulin production, possible Type 1 or LADA | |
| > 5.0 ng/mL | Elevated levels, often due to obesity or insulin resistance |
When Should You Consider the C-Peptide Test?
You may be advised to take a C-peptide assay if:
- Your diabetes type is unclear (e.g., LADA vs Type 2)
- You are not responding to insulin therapy as expected
- Your doctor is planning to switch you from insulin to oral medications
- You need an assessment of remaining beta-cell function
Factors to Consider Before the Test
For Fasting Test:
- Do not eat or drink anything except water for 8–10 hours
- Avoid insulin injections before the test unless advised
For Stimulated Test:
- A standard glucose drink or carbohydrate-rich meal will be given
- Blood is drawn after 90 minutes
- Avoid taking insulin, sulfonylureas, or GLP-1 agonists before the test (unless instructed)
- Inform your doctor about all current medications
Why the C-Peptide Assay Is Crucial in Diabetes Care
The C-peptide test provides real-time insights into how your pancreas functions, helping your care team:
- Diagnose the correct type of diabetes
- Tailor individualised treatment plans
- Avoid unnecessary insulin therapy
- Choose between oral drugs, injectables, or combination therapies
- Predict the progression of the disease
Book Your C-Peptide Assay at Dr. Mohan’s
At Dr. Mohan’s Diabetes Specialities Centre, we offer both fasting and stimulated C-peptide assays as part of our comprehensive diagnostic packages. Our specialists ensure accurate interpretation and personalised advice based on your test results.
Explore our diagnostic packages
Book your C-Peptide Test now