Quick Facts
- Sample: Blood serum
- Fasting: 14–16 hours required
- Turn-around: 1-2 business days. May take longer based on weather, holiday, or lab delays.
Benefits
- Accurate insulin assessment - Measures your body's natural insulin production even if taking insulin therapy
- Diabetes type clarity - Helps distinguish between type 1 and type 2 diabetes for proper treatment
- Superior testing reliability - More accurate than direct insulin measurement, especially with insulin antibodies
- Convenient monitoring - Track pancreatic function over time without multiple doctor visits
- Hypoglycemia investigation - Identifies underlying causes of unexplained low blood sugar episodes
- Cost-effective solution - Direct access without prescription requirements or physician consultations
Who Is This Test For?
- Diabetic patients taking insulin who want to assess remaining pancreatic function
- Newly diagnosed diabetics seeking clarity between type 1 and type 2 classification
- Hypoglycemia sufferers experiencing unexplained low blood sugar episodes
- Health monitors tracking metabolic changes and insulin resistance over time
- Tumor suspects investigating possible insulinomas or pancreatic insulin-secreting tumors
- Treatment optimizers wanting to make informed decisions about diabetes management approaches
How It Works – Just 3 Steps
- Fast and prepare - Fast for 14-16 hours, discontinue biotin supplements 72 hours prior
- Visit lab for draw - Simple blood draw at any participating collection site
- Receive results - Confidential electronic results delivered within 1 business day
FAQ
What exactly does C-peptide measure? C-peptide measures your pancreas's natural insulin production. Since insulin and C-peptide are released in equal amounts, but C-peptide stays in your bloodstream longer, it provides an accurate assessment of endogenous insulin production (American Diabetes Association 2024).
Can I take this test while on insulin therapy? Yes, that's actually when C-peptide testing is most valuable. Unlike direct insulin tests, C-peptide specifically measures your body's own insulin production, not injected insulin, making it perfect for insulin-dependent patients (Alberta Health Services 2024).
Will my diabetes medications affect the results? Some diabetes medications can influence results, and biotin supplements must be stopped 72 hours before testing. Always inform the laboratory about all medications you're taking for accurate interpretation (Request A Test 2025).
How long does fasting take and what can I drink? You need to fast for 14-16 hours before the test, consuming only water during this period. Schedule your test in the morning to make fasting more manageable.
What if my results are abnormal? Share results with your healthcare provider for proper interpretation within your health context. Abnormal levels may indicate need for further testing or treatment adjustments based on your specific situation.
More Details
What is the purpose of this test?
The C-Peptide Serum Test measures your pancreas's ability to produce insulin naturally. Since C-peptide is released in equal amounts with insulin but remains in circulation longer, it provides a reliable assessment of endogenous insulin production. This test is particularly valuable because it distinguishes between your body's own insulin and any injected insulin therapy, offering clear insights into pancreatic beta cell function (Practical Diabetes International 2017).
Who would benefit from this test?
This test benefits individuals with diabetes, especially those taking insulin who need to understand their remaining pancreatic function. It's valuable for patients with unexplained hypoglycemia, those with unclear diabetes classification, and people suspected of having insulinomas or other pancreatic tumors. Health-conscious individuals monitoring metabolic changes and insulin resistance patterns also find this test informative for proactive health management (Alberta Health Services 2024).
When should I order a C-Peptide Serum Test?
Consider ordering when you need to determine if your pancreas produces adequate insulin, differentiate between diabetes types, investigate unexplained low blood sugar episodes, monitor pancreatic function during treatment, or assess for possible insulin-secreting tumors. The test is also recommended when insulin antibodies might interfere with direct insulin measurements, making C-peptide a more reliable biomarker.
How do I interpret the results?
C-peptide below 0.2 nmol/L
- What it means: Significant insulin deficiency (Type 1 diabetes)
- Typical action: Insulin therapy required
C-peptide 0.2–1.1 nmol/L
- What it means: Normal pancreatic function
- Typical action: Continue monitoring
C-peptide above 1.1 nmol/L
- What it means: Possible insulin resistance (Type 2 diabetes)
- Typical action: Lifestyle modifications, medication review
C-peptide extremely high levels
- What it means: Possible insulinoma or tumor
- Typical action: Further investigation needed
C-peptide testing shows 29% higher sensitivity with glucagon stimulation compared to 19% with postprandial testing, making stimulated testing more diagnostically valuable (Practical Diabetes International 2017).
Disclaimer: Reference ranges may vary by laboratory. Listed ranges are general guidelines and may differ from those used by the performing lab. Always consult your healthcare provider for interpretation.
Pre-test preparation
Fast for 14-16 hours before your test, consuming only water during this period. Discontinue biotin supplements at least 72 hours prior to testing, as they can interfere with results. Consult your healthcare provider about temporarily adjusting diabetes medications that might affect outcomes. Schedule your appointment in the morning to accommodate fasting requirements more comfortably.
How often should I get tested?
- Newly diagnosed diabetes – Baseline, then 6 months
- Monitoring pancreatic function – Every 6–12 months
- Insulin therapy initiation – Before starting, then annually
- Unexplained hypoglycemia – As needed for episodes
- Treatment optimization – Every 3–6 months
Why early detection matters
Early C-peptide testing helps preserve pancreatic function by enabling timely intervention strategies. Understanding your insulin production capacity allows for personalized treatment approaches, whether focusing on beta cell preservation in early diabetes or optimizing therapy in established cases. Identifying declining C-peptide levels early can prevent complications and guide lifestyle modifications that support remaining pancreatic function (Journal of Diabetes and Its Complications 2025).
Related tests you may consider
Insulin Blood Test - Complements C-peptide results for calculating insulin resistance indices and comprehensive metabolic assessment
HbA1c Test - Provides 3-month glucose control average, essential for complete diabetes management picture
Glucose Tolerance Test, 2-Hour - Offers dynamic blood sugar regulation assessment over a specified time.
