Insulin and C-Peptide Ratio

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)

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).