Calcium infusion: a new provocative test for insulinomas

Area of Science:

• Endocrinology
• Clinical Diagnostics
• Oncology

Background:

• Hypoglycemia, particularly when caused by insulinomas, presents a diagnostic challenge.
• Accurate diagnosis is crucial for effective treatment and management of insulin-secreting tumors.

Purpose of the Study:

• To evaluate the efficacy of intravenous calcium gluconate infusion as a provocative test for diagnosing insulinomas.
• To determine if calcium infusion can differentiate insulinomas from other causes of hypoglycemia.

Main Methods:

• Intravenous administration of calcium gluconate (10 mg Ca(++)/kg) over 2 hours to 16 adult patients.
• Monitoring of serum glucose, insulin, proinsulin, and C-peptide levels before and during calcium infusion.
• Comparison of responses in patients with insulinomas, islet cell hyperplasia, reactive hypoglycemia, and healthy volunteers.

Main Results:

• Nine of ten patients with insulinomas experienced significant hypoglycemia and hyperinsulinemia within 60-90 minutes of calcium infusion.
• Elevated serum proinsulin and C-peptide levels were observed during calcium-induced hyperinsulinemia in several patients.
• No significant changes in glucose or insulin levels were observed in patients with other forms of hypoglycemia or in healthy volunteers.
• Calcium infusion was ineffective in a patient with a benign insulinoma whose tumor was already maximally secreting.

Conclusions:

• Intravenous calcium gluconate infusion is a safe, rapid, and effective provocative test for diagnosing insulin-secreting islet cell tumors (insulinomas).
• The test reliably differentiates insulinomas from other causes of hypoglycemia, including islet cell hyperplasia and reactive hypoglycemia.