Secretin Stimulation Test

• The Secretin Stimulation Test assesses the exocrine function of the pancreas.
• It helps diagnose conditions like chronic pancreatitis and gastrinoma (Zollinger-Ellison syndrome).
• The procedure involves intravenous administration of secretin and collection of pancreatic fluid or blood samples.
• Results are interpreted by measuring bicarbonate and enzyme levels in pancreatic fluid, or gastrin levels in blood.
• Abnormal results can indicate pancreatic insufficiency or excessive gastrin production.

What is the Secretin Stimulation Test?

The Secretin Stimulation Test is a medical diagnostic procedure designed to evaluate the exocrine function of the pancreas. The pancreas, an organ located behind the stomach, produces digestive enzymes and bicarbonate, which are crucial for breaking down food in the small intestine. Secretin is a hormone naturally released by the small intestine in response to acidic chyme entering from the stomach. Its primary role is to stimulate the pancreas to release bicarbonate-rich fluid, which neutralizes stomach acid and creates an optimal environment for digestive enzymes.

During this test, synthetic secretin is administered to observe the pancreatic response. This allows clinicians to measure the pancreas’s ability to produce and secrete bicarbonate and, in some cases, digestive enzymes. It is considered a highly sensitive and specific test for assessing pancreatic exocrine function, particularly in cases where other imaging or blood tests may be inconclusive.

Purpose and Procedure of the Test

The purpose of Secretin Stimulation Test is primarily to diagnose conditions affecting the pancreas, such as chronic pancreatitis, and to identify certain types of pancreatic tumors like gastrinomas (Zollinger-Ellison syndrome). In chronic pancreatitis, the pancreas becomes inflamed and damaged, leading to impaired enzyme and bicarbonate production. For gastrinomas, the test helps confirm the diagnosis by measuring an exaggerated gastrin response to secretin, as these tumors produce excessive gastrin, a hormone that stimulates stomach acid production.

The secretin stimulation test procedure typically involves several steps, often performed in a hospital or specialized outpatient setting:

• A small tube, called an endoscope or a nasogastric tube, is carefully advanced through the nose or mouth, down the esophagus and stomach, and into the duodenum (the first part of the small intestine).
• Pancreatic fluid samples are collected from the duodenum through this tube to establish baseline levels.
• Synthetic secretin is then administered intravenously (into a vein).
• Additional samples of pancreatic fluid are collected at regular intervals (e.g., every 15-30 minutes) for up to two hours after secretin administration.
• Alternatively, for suspected gastrinoma, blood samples are drawn at intervals to measure gastrin levels.

The collected samples are then sent to a laboratory for analysis of bicarbonate concentration, enzyme levels (like amylase and lipase), or gastrin levels, depending on the specific diagnostic goal.

Interpreting Secretin Stimulation Test Results

Understanding secretin stimulation test results explained is crucial for an accurate diagnosis. The interpretation depends on what is being measured:

For pancreatic exocrine function (e.g., suspected chronic pancreatitis), the primary measurement is the bicarbonate concentration in the collected duodenal fluid. Normal results typically show a significant increase in bicarbonate secretion following secretin administration, indicating a healthy pancreatic response. Abnormally low bicarbonate levels suggest pancreatic insufficiency, a common feature of chronic pancreatitis, cystic fibrosis, or pancreatic cancer that obstructs the ducts. The specific threshold for bicarbonate concentration can vary slightly between laboratories but generally, values below a certain level (e.g., <80 mEq/L) are considered indicative of impaired function.

For suspected gastrinoma (Zollinger-Ellison syndrome), blood gastrin levels are measured. In healthy individuals, secretin typically has little to no effect on gastrin levels, or may even cause a slight decrease. However, in patients with a gastrinoma, secretin administration causes a paradoxical and significant increase in serum gastrin levels, often rising by more than 200 pg/mL from baseline. This exaggerated response is a hallmark of gastrin-producing tumors and helps differentiate them from other causes of high gastrin levels.