What are possible findings on an insulin test?

Updated: Jan 02, 2019
  • Author: Saranya Buppajarntham, MD; Chief Editor: Eric B Staros, MD  more...
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Answer

Answer

Insulin testing is used to assist in identifying causes of hypoglycemia (plasma glucose levels < 55 mg/dL), especially upon signs and symptoms of hypoglycemia (neurohypoglycopenic and autonomic symptoms). In this scenario, a 72-hour fasting test is performed. [2]

  • Insulinoma: High insulin and C-peptide levels

  • Non–beta cell tumors: Low insulin and C-peptide levels and high insulinlike growth factor 2 level [3]

  • Excessive insulin administration: High insulin levels and low C-peptide levels

  • Insulin secretagogue administration (sulfonylurea and glinides): High insulin and C-peptide levels

  • Congenital hyperinsulinism (mutation in insulin-secreting gene): High insulin and C-peptide levels

  • Autoimmunity to insulin or insulin receptor (common in patients receiving insulin or those who have autoimmune diseases such as systemic lupus erythematosus [SLE] or Hashimoto thyroiditis): Postprandial insulin is bound to antibodies and dissociated 1 hour later, resulting in an extremely elevated insulin level and high insulin–to–C-peptide ratio [4]

Table 2. Interpretation of 72-hour Fasting Test Results [2] (Open Table in a new window)

Condition

Insulin

C-Peptide

Proinsulin

Insulinlike Growth Factor 2

Sulfonylurea

Glucose Level After Administration of Glucagon

Insulinoma

Non–beta cell tumors

Insulin injection

Sulfonylurea-induced


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