Why test C-Peptide instead of insulin?

C-Peptide testing has several advantages: it is not affected by insulin injections (since C-Peptide only comes from your own insulin production), it has a longer half-life so levels are more stable, and it is not affected by insulin antibodies that can interfere with insulin tests. This makes it a more reliable marker of your pancreas's insulin-producing capacity.

Can C-Peptide help determine if I need insulin?

Yes, in people with Type 2 diabetes, C-Peptide levels can help assess remaining beta cell function. Low levels suggest your pancreas is no longer producing enough insulin and insulin therapy may be needed. Higher levels suggest oral medications may still be effective.

What causes very high C-Peptide levels?

Very high C-Peptide may indicate insulinoma (a rare insulin-producing tumor), Type 2 diabetes with significant insulin resistance (the pancreas overproduces insulin trying to overcome resistance), or kidney disease (which reduces C-Peptide clearance). Clinical context is important for interpretation.

Can C-Peptide predict honeymoon phase in Type 1 diabetes?

Yes, C-Peptide can help assess the "honeymoon phase" in newly diagnosed Type 1 diabetes—a period when the pancreas still produces some insulin. Measurable C-Peptide during this time may allow for better blood sugar control with less insulin. As Type 1 diabetes progresses, C-Peptide typically becomes undetectable.

🩸 Diabetes

C-Peptide Blood Test

Name: C-Peptide Blood Test
Brand: Justlabs
SKU: 0000380
Price: 10 USD
Availability: InStock

C-Peptide

C-Peptide is a byproduct of insulin production that provides a reliable measure of how much insulin your pancreas is making, helping to classify diabetes type and assess beta cell function.

C-Peptide is a protein fragment that is released into the bloodstream when the pancreas produces insulin. For every molecule of insulin made, one molecule of C-Peptide is created. Because C-Peptide is cleared from the body more slowly than insulin and is not affected by insulin injections, it provides a more stable and accurate measurement of endogenous (your own) insulin production. This test is particularly valuable for distinguishing between Type 1 diabetes (where insulin production is minimal or absent) and Type 2 diabetes (where insulin may be normal or elevated but less effective). It can also help assess remaining beta cell function in people with diabetes and evaluate unexplained low blood sugar.

Price

$10

Results

2-3 days

Lab Network

Quest

Fasting

8+ hrs

What's Measured

C-Peptide

What This Test Measures

This test measures the level of C-Peptide in your blood. C-Peptide levels directly reflect how much insulin your pancreas is producing. Low levels indicate reduced insulin production (as in Type 1 diabetes), while normal or high levels suggest adequate insulin production (as in early Type 2 diabetes or insulin resistance).

Who Should Consider This Test

People with newly diagnosed diabetes to determine type (Type 1 vs Type 2), those with Type 2 diabetes to assess if insulin therapy is needed, people with hypoglycemia to determine if it is caused by excess insulin production, and individuals with Type 1 diabetes to evaluate remaining beta cell function.

Health Insights

Conditions Screened

Type 1 diabetesType 2 diabetesInsulinoma (insulin-producing tumor)Hypoglycemia evaluationBeta cell function assessmentInsulin resistance

Related Symptoms

Classifying diabetes typeEvaluating insulin production capacityInvestigating hypoglycemia causesAssessing need for insulin therapyMonitoring beta cell function

When to Get Tested

Fasting for 8-12 hours is required for accurate results. A fasting C-Peptide reflects baseline insulin production. Sometimes a stimulated C-Peptide test (after a meal or glucose drink) may be ordered to assess maximum insulin capacity.

Fasting Required

This test requires fasting for accurate results. Please follow these instructions:

Do not eat or drink anything except water for 8-12 hours before your blood draw.
Water is allowed and encouraged - stay hydrated!
Schedule your lab visit in the morning for convenience.
Continue taking any prescribed medications unless advised otherwise by your doctor.

Understanding Your Results

Normal fasting C-Peptide levels typically range from 0.5-2.0 ng/mL. Very low or undetectable levels (<0.2 ng/mL) strongly suggest Type 1 diabetes or advanced Type 2 diabetes with beta cell failure. Normal or elevated levels with high blood sugar suggest insulin resistance (Type 2 diabetes). Very high levels may indicate insulinoma or other insulin-secreting conditions.

What to Expect

After placing your order, you'll receive an email from Rupa Health (our lab order partner) within 24 business hours to sign a consent form and schedule your blood draw at a Quest Diagnostics location.

The blood draw typically takes just a few minutes. Results are usually available within 2-3 business days and will appear in your secure Justlabs dashboard.

Our results include reference ranges and easy-to-understand indicators showing whether your values are within normal limits.

Frequently Asked Questions

$10

Typical hospital cash price: $150–$250

+ $28 in standard lab & physician fees at checkout (no additional bills later)

$18 lab collection + $10 physician order

Results in 2-3 business days

Fasting required (8+ hours)

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