Which test is important in diagnosing gastric acid hypersecretion for Zollinger-Ellison syndrome?

The secretin test is critical in diagnosing Zollinger-Ellison syndrome, which is characterized by excessive gastric acid production usually due to gastrin-secreting tumors. In this test, secretin, a hormone produced by the intestines, is administered to the patient. In individuals with Zollinger-Ellison syndrome, the administration of secretin will lead to a significant increase in serum gastrin levels inappropriately, as the excessive gastrin production is a hallmark of the condition.

This responsiveness to secretin is what distinguishes Zollinger-Ellison syndrome from other conditions that may cause high gastrin levels, such as ulcers or other gastrointestinal disorders. By confirming elevated gastrin levels in response to secretin, this test supports the diagnosis of the syndrome.

Other tests mentioned are not as relevant for diagnosing this specific condition. The hemoglobin A1c test is primarily for monitoring diabetes, the upper GI series helps visualize structural issues in the gastrointestinal tract, and pH monitoring primarily assesses acid reflux rather than hypersecretion conditions. Therefore, the secretin test stands out as the most direct and effective method for diagnosing gastric acid hypersecretion in this syndrome.