Test Talk: Gastrin

When a physician orders a gastrin level, he/she is typically diagnosing peptic ulcers, gastritis, bowel obstruction, diarrhea, or abdominal pain. It is also used to diagnose Zollinger-Ellison (Z-E) Syndrome, a condition associated with the formation of pancreatic and duodenal tumors that produce excess gastrin. 

Gastrin is a hormone. Normally it's produced in the stomach and regulates acid production during digestion. The gastrin level in the blood is diurnal (changes according to the time of day). It's at its highest during the day and lowest between 3 and 7 a.m. It also rises and falls in the blood stream according to food intake. When the patient fasts, gastrin rises in the blood. After meals, it relocates to the gut where its needed. When the serum gastrin is elevated, interpretation must include an analysis of the gastrin within the patient's gastric contents. 

When patients develop "gastrinomas", i.e., tumors that produce an overabundance of gastrin, (ZE Syndrome), it leads to multiple complications including peptic ulcers, the discomfort from which is what typically prompts patients to seek medical evaluation. However, most stomach ulcers are not due to gastrinomas, but Helicobacter pylori infections.

More than half of gastrinomas are malignant, causing cancer that can spread to other parts of the body. That's why it's important to make sure samples are drawn and processed precisely as recommended. Disregarding the fasting requirement and sample handling specifics can prevent the physician from diagnosing the condition, potentially causing a life-threatening delay in diagnosis and treatment.

Gastrin samples are typically drawn from patients who have fasted for 12 hours and restricted alcohol intake for 24 hours. The sample is drawn into heparinized tubes, but serum is acceptable in some systems. (Always follow your facility's sample requirements.) Regardless of the tube, gastrin is only stable for two hours, and must be immediately placed on ice for transport. The sample should be centrifuged in less than two hours and the serum/plasma frozen or tested immediately.   

Bibliography:

• LabTestsOnline. American Association for Clinical Chemistry. AACC. www.labtestsonline.org. Accessed 3/6/2019.
• Wu A. Tietz Clinical Guide to Laboratory Tests---Fourth Edition. Elsevier. St. Louis, Missouri. 2006. 
• World Health Organization. Use of Anticoagulants in Diagnostic Laboratory Investigations. WHO. Geneva, Switzerland. 2002.