Insulin–to–C-Peptide Ratio

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Subject: Insulin–to–C-Peptide Ratio

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Definition

  • Insulin and C-peptide are secreted into portal vein in equimolar amounts, but serum ratio = 1:5 to 1:15 due to removal of approximately 50% of insulin from blood during initial passage through the liver. C-peptide half-life = approximately 30 minutes.

  • Normal range: fasting molar ratio insulin to C-peptide = 1.0.

Use

  • To differentiate insulinoma from factitious hypoglycemia due to insulin

Interpretation

  • Less than 1.0 in molarity units (or >47.17 μg/ng in conventional units)

    • Increased endogenous insulin secretion (e.g., insulinoma, sulfonylurea administration)

    • Renal failure

  • Greater than 1.0 in molarity units (or <47.17 μg/ng in conventional units)

    • Exogenous insulin administration

    • Cirrhosis

Limitations

  • There are ethnic differences in insulin/C-peptide ratio in both fasting and glucose-stimulated conditions in normal young nondiabetic pregnant women. Compared with their Caucasian and Hispanic counterparts, African American women had indices suggestive of lower insulin production and greater insulin resistance (i.e., a lower C-peptide concentration, a lower C/I ratio, and elevations in insulin and the I/G ratio).

 
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