In cases of insulinoma, what levels of insulin and C-peptide are expected?

In cases of insulinoma, a type of pancreatic tumor that secretes insulin, the expected findings are high levels of both insulin and C-peptide. Insulin is produced by the beta cells of the pancreas, and C-peptide is a byproduct of insulin synthesis. When insulin is secreted, C-peptide levels rise in parallel because they are both released from the same proinsulin precursor molecule.

In insulinoma, the tumor drives excessive production of insulin regardless of blood glucose levels, leading to hyperinsulinemia (high levels of insulin). Because the pancreatic beta cells are actively producing insulin, there is also an increase in C-peptide, indicating that the endogenous production of insulin is taking place.

This pattern contrasts with other conditions such as exogenous insulin administration, where insulin levels can be high while C-peptide levels remain low due to lack of endogenous insulin production. Similarly, in conditions of insulin resistance or type 2 diabetes, while insulin levels may be elevated, C-peptide could be variable depending on the stage of the disease. Hence, the correct expectation in insulinoma is a simultaneous elevation of both insulin and C-peptide levels.