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Difficulty: HardEndocrinology and Metabolism

A patient is being evaluated for recurrent fasting hypoglycemia. Match the following diagnostic laboratory profiles (obtained during a symptomatic hypoglycemic episode with plasma glucose << 5555 mg/dL) with their most likely underlying etiology.

  • Elevated insulin, decreased C-peptide, decreased beta-hydroxybutyrate, negative hypoglycemic drug screenExogenous insulin administration
  • Elevated insulin, elevated C-peptide, decreased beta-hydroxybutyrate, negative hypoglycemic drug screenInsulinoma (pancreatic beta-cell tumor)
  • Elevated insulin, elevated C-peptide, decreased beta-hydroxybutyrate, positive hypoglycemic drug screenSulfonylurea or meglitinide ingestion
  • Decreased insulin, decreased C-peptide, elevated beta-hydroxybutyrate, negative hypoglycemic drug screenGlucocorticoid deficiency (or prolonged starvation)

Answer

Properly map each fasting hypoglycemia laboratory profile to exogenous insulin, insulinoma, sulfonylurea ingestion, and glucocorticoid deficiency respectively based on insulin, C-peptide, beta-hydroxybutyrate, and drug screen findings.
The diagnostic workup for fasting hypoglycemia systematically measures insulin, C-peptide, beta-hydroxybutyrate, and a hypoglycemic drug screen. Exogenous insulin lacks C-peptide, leading to high insulin but suppressed C-peptide. Insulinoma and sulfonylurea toxicity both cause endogenous insulin secretion (high insulin and high C-peptide), but are differentiated by the positive drug screen in the latter. All three hyperinsulinemic states suppress lipolysis, resulting in low beta-hydroxybutyrate. Conversely, glucocorticoid deficiency or prolonged starvation causes hypoinsulinemic hypoglycemia, where insulin and C-peptide are appropriately suppressed, allowing unimpeded lipolysis and elevated beta-hydroxybutyrate production.

Step-by-Step Solution

1
Analyze the relationship between serum insulin and C-peptide levels.
Endogenous insulin secretion produces equimolar amounts of C-peptide. Exogenous pharmaceutical insulin does not contain C-peptide.
This fundamentally differentiates exogenous hyperinsulinemia (low C-peptide) from endogenous causes (high C-peptide).
2
Evaluate the beta-hydroxybutyrate (ketone) levels.
Beta-hydroxybutyrate is a ketone body whose production via lipolysis is strictly suppressed by insulin. Elevated levels indicate a hypoinsulinemic state.
This separates hyperinsulinemic hypoglycemia (insulinoma, sulfonylurea, exogenous insulin), which all have low ketones, from hypoinsulinemic hypoglycemia (starvation, glucocorticoid deficiency), which has high ketones.
3
Review the hypoglycemic agent screen in endogenous hyperinsulinemic states.
A positive screen confirms secretagogue ingestion, while a negative screen points to a primary endogenous source such as an insulinoma.
Sulfonylureas and insulinomas have identical insulin and C-peptide profiles; the drug screen is specifically required to distinguish them.

Key Concept

The diagnostic evaluation of fasting hypoglycemia relies on differentiating endogenous versus exogenous hyperinsulinemia (via C-peptide) and determining the presence of insulin action (via beta-hydroxybutyrate).
Estimated Time:1m 30s
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Topics

Endocrinology and Metabolism

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