C-Peptide (Connecting Peptide) (C-Peptide)
C-Peptide is the 31-amino-acid peptide cleaved from proinsulin in equal equimolar ratio to endogenous insulin. Because it bypasses first-pass hepatic extraction, it provides the true measure of endogenous pancreatic beta-cell reserve.
Standard vs. Optimal Reference Rangesng/mL
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Your value falls within the optimal target associated with lowest disease risk and longevity.
0.8 - 3.1 ng/mL
General reference distribution across unselected commercial populations.
1.0 - 2.0 ng/mL
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
Proinsulin is processed in secretory granules by prohormone convertases PC1/3 and PC2, yielding mature insulin and C-peptide. Unlike insulin (50% extracted by liver on first pass), C-peptide has a longer circulating half-life (30 minutes) and is cleared exclusively by the kidneys.
Differential Diagnosis
Elevated Levels (C-Peptide High)
- •Insulinoma
- •Type 2 Diabetes Mellitus with compensatory hypersecretion
- •Renal impairment (reduced clearance)
Low Levels (C-Peptide Low)
- •Type 1 Diabetes Mellitus (absolute beta-cell failure)
- •Exogenous insulin administration (factitious hypoglycemia)
- •Pancreatic exhaustion
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Strict 10 to 12 hour overnight water-only fasting is mandatory for baseline metabolic quantification. Acute psychological stress, acute infectious illness, and sleep deprivation (<6 hours) transiently elevate cortisol and catecholamines, falsely elevating glycemic markers. For glucose and insulin testing, draw blood into sodium fluoride/potassium oxalate tubes or separate serum promptly within 30 minutes to prevent ongoing in vitro red blood cell glycolysis.
Reflexive Testing Protocol:
- Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and HOMA-Beta calculations
- Continuous Glucose Monitoring (CGM) 14-day wear to evaluate glycemic variability and postprandial excursions
- Fasting C-Peptide and high-sensitivity Troponin/hs-CRP to differentiate insulin resistance from beta-cell exhaustion
- Oral Glucose Tolerance Test (OGTT) with simultaneous 0, 30, 60, and 120-minute insulin assays
- Abdominal ultrasound or FibroScan to evaluate hepatic steatosis and non-alcoholic fatty liver disease (MASLD)
Clinical Citations & Primary Literature (1)
- [1]C-Peptide as a Key Biomarker in Diabetes Care and Research - Diabetes Care (2022). PMID: 35020815
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate C-Peptide (Connecting Peptide) (C-Peptide) into overall healthspan optimization.