C-Peptide Fasting Serum Test
Short Name: C-Peptide Fasting
Also known as: C-Peptide Serum Test, Fasting C-Peptide Test, Connecting Peptide Test, Proinsulin C-Peptide Test
C-Peptide Fasting Serum Test test available at DNA Labs India for ₹1,229. Uses Chemiluminescent Immunoassay on Serum samples. Results in Same Day. Free home collection in 300+ cities across India.
🩺 Medically Reviewed By
Dr Ramarao Paidisetty
Consultant Biochemist · Reg: 21504
Last reviewed: September 7, 2026
Overview
The primary purpose of the C-Peptide Fasting Serum Test is to evaluate how much insulin your pancreas is producing. It helps clinicians distinguish between Type 1 and Type 2 diabetes, assess residual beta-cell function in known diabetics, investigate unexplained episodes of low blood sugar (hypoglycemia), and detect insulin-producing tumors such as insulinomas. This test is also useful for determining whether a patient requires insulin therapy or can be managed with oral medications alone.
- Test Code
- 368
- Price
- ₹1,229
- Sample Type
- Serum
- Result Time
- Same Day
- Fasting Required
- Yes (10 hours)
- Method
- Chemiluminescent Immunoassay
Sample Collection
Overnight fasting for at least 10-12 hours is mandatory before sample collection. Inform your physician about all medications you are currently taking, as certain drugs may influence test results. Avoid strenuous physical activity the evening before and morning of the test. Stay hydrated by drinking plain water during the fasting period.
Method: Venipuncture
Laboratory Analysis
A blood sample will be drawn from a vein in your arm (venipuncture) using a sterile needle. The blood is collected into a Serum Separator Tube (SST). The procedure typically takes only a few minutes and involves minimal discomfort, similar to a standard blood draw.
Report Delivery
After blood collection, pressure will be applied to the puncture site with a cotton ball or bandage. You may resume normal activities and eating immediately after sample collection. Mild bruising at the needle site is common and resolves on its own. Results are typically available the same day.
Timeline: Same Day
Patient Instructions
About This Test
Who Should Get This Test
The primary purpose of the C-Peptide Fasting Serum Test is to evaluate how much insulin your pancreas is producing. It helps clinicians distinguish between Type 1 and Type 2 diabetes, assess residual beta-cell function in known diabetics, investigate unexplained episodes of low blood sugar (hypoglycemia), and detect insulin-producing tumors such as insulinomas. This test is also useful for determining whether a patient requires insulin therapy or can be managed with oral medications alone.
How to Prepare
- Overnight fasting for 10-12 hours is mandatory before sample collection
- Drink only plain water during the fasting period; avoid tea, coffee, and juice
- Avoid strenuous exercise 24 hours before the test
- Inform the phlebotomist about any medications you are taking
- 2 mL (minimum 0.5 mL) of serum is required from 1 SST tube
- Ship the sample refrigerated or frozen to the laboratory
- Wear a short-sleeved shirt or loose-fitting sleeves for easy venipuncture access
Doctor's Notes
Reviewed by Dr Ramarao Paidisetty — MBBS, MD (Biochemistry) · Reg. No. 21504
"The C-Peptide Fasting Serum Test is one of the most valuable tools in my clinical practice for differentiating between Type 1 and Type 2 diabetes. Unlike direct insulin measurement, C-peptide is not affected by exogenous insulin injections, making it a more accurate reflection of the pancreas's own insulin-producing capacity. A low fasting C-peptide level in a diabetic patient strongly suggests Type 1 diabetes or late-stage Type 2 diabetes with beta-cell exhaustion, while a normal or elevated level typically points to Type 2 diabetes with insulin resistance. I also rely on this test when evaluating unexplained hypoglycemia, suspected insulinomas, and when assessing residual beta-cell function. I recommend this test for any patient with newly diagnosed diabetes or when there is uncertainty about the diabetes type."
Last medically reviewed: September 7, 2026
Test Parameters & Specifications
Sample Stability
- Non-fasting sample (overnight fasting is mandatory)
- Insufficient sample volume (less than 0.5 mL serum)
- Hemolyzed, lipemic, or icteric sample
- Improperly labeled or unlabeled sample
- Sample received beyond stability period
- Sample stored at incorrect temperature
Understanding Your Results
Fasting C-peptide levels within the normal range suggest adequate insulin production by the pancreas. This is typically seen in healthy individuals.
Status: Normal
Range: 0.8 - 3.9 ng/mL
Elevated fasting C-peptide levels may indicate Type 2 diabetes with insulin resistance, insulinoma (insulin-producing tumor), Cushing's syndrome, kidney disease (reduced clearance), or use of sulfonylurea medications. Obesity can also cause elevated levels.
Status: High
Range: > 3.9 ng/mL
Low fasting C-peptide levels suggest reduced or absent insulin production. This is commonly seen in Type 1 diabetes, late-stage Type 2 diabetes with beta-cell exhaustion, or in patients with exogenous insulin-induced hypoglycemia. It may also indicate severe pancreatic damage.
Status: Low
Range: < 0.8 ng/mL
Consult your physician or endocrinologist if your C-peptide test results are outside the normal reference range. A low C-peptide level may indicate Type 1 diabetes or significant pancreatic damage requiring insulin therapy. A high level may suggest Type 2 diabetes with insulin resistance, requiring a different treatment approach. If you experience symptoms such as frequent urination, excessive thirst, unexplained weight loss, recurrent episodes of low blood sugar, or blurred vision, seek medical advice promptly for comprehensive evaluation and appropriate management.
Limitations
- ⚠C-peptide levels may not accurately reflect insulin production in patients with significant renal impairment
- ⚠Single fasting measurement may not capture dynamic insulin secretion patterns
- ⚠Results should always be interpreted alongside clinical symptoms and other diagnostic tests
- ⚠C-peptide levels can vary between laboratories due to differences in assay methods
- ⚠This test does not measure insulin resistance directly
Risks & Considerations
- ●Minor bruising or swelling at the needle insertion site
- ●Slight pain or discomfort during venipuncture
- ●Rarely, dizziness or lightheadedness during blood draw
- ●Very rare risk of infection at the puncture site
Interfering Factors
- ●Recent exogenous insulin administration may affect interpretation
- ●Kidney disease or impaired renal function can elevate C-peptide levels due to reduced clearance
- ●Severe liver disease may alter C-peptide metabolism
- ●Obesity can cause elevated C-peptide levels due to insulin resistance
- ●Medications such as sulfonylureas can stimulate C-peptide secretion
- ●Hemolyzed blood samples may affect test accuracy
Compare With Similar Tests
| Test | C-Peptide Fasting Serum Test | ||||
|---|---|---|---|---|---|
| Comparison | C-Peptide Fasting Serum Test | Both tests assess insulin production, but the C-peptide test is preferred for patients on exogenous insulin therapy because C-peptide is not affected by injected insulin. The fasting insulin test measures insulin directly and can give misleading results in insulin-treated patients. | HbA1c measures average blood sugar levels over the past 2-3 months and reflects long-term glucose control. The C-peptide test measures current insulin production capacity. Both are complementary: HbA1c tells you about blood sugar control while C-peptide tells you about the underlying insulin production. | FPG measures blood sugar levels at a single point in time after fasting. It indicates whether blood sugar is elevated but does not explain why. The C-peptide test reveals whether the pancreas is producing adequate insulin, helping to determine the cause of abnormal blood sugar. | OGTT measures how the body processes a glucose load over 2-3 hours and is used to diagnose diabetes and gestational diabetes. C-peptide testing evaluates insulin production at baseline. OGTT is more comprehensive for detecting impaired glucose tolerance, while C-peptide helps classify the type of diabetes. |
Frequently Asked Questions
What is a C-Peptide Fasting Serum Test?
Why is overnight fasting required for the C-Peptide test?
What does a high C-Peptide level indicate?
What does a low C-Peptide level indicate?
How is the C-Peptide test different from a fasting insulin test?
What is the cost of the C-Peptide Fasting Serum Test at DNA Labs India?
How long does it take to get C-Peptide test results?
Can the C-Peptide test distinguish between Type 1 and Type 2 diabetes?
Is the C-Peptide Fasting Serum Test painful?
Are there any risks associated with the C-Peptide test?
Can I take my medications before the C-Peptide Fasting Serum Test?
Is home sample collection available for the C-Peptide Fasting Serum Test?
Related Tests
Reference Laboratory Services
We serve as a reference laboratory for hospitals and clinics across India. Send samples from your facility with same-day pickup, priority processing, and results delivered through our online portal. Competitive institutional pricing available.
Your Data Privacy
Your medical data is protected under Indian law.
✓ Stored in India: All patient records are stored on servers located in India. No data is transferred outside the country.
✓ DPDP Act Compliant: Under the Digital Personal Data Protection Act 2023, you can request deletion of your records at any time by contacting support.
Book Your Test
Enter your details and we'll connect you within 15 minutes.