Gastrin A peptide hormone secreted by the G cells of the gastric antral Description mucosa. Diagnosis of gastrinoma in patients with gastric acid hypersecretion, for example in Zollinger-Ellison (ZE) syndrome. May also be helpful Indication in the evaluation of patients with suspected antral G-cell hyperplasia or atrophic gastritis. There are three molecular forms of gastrin that stimulate gastric acid secretion: big gastrin (G-34, the principal component in healthy individuals), little gastrin (G-17) and mini gastrin (G-14). G-71, G-52 and G-6 are also present in small amounts.

Gastrin is secreted physiologically in response to several stimuli, Additional Info including antral distension following eating a meal, amino acids and peptides from partially digested proteins in the stomach, vagal stimulation, caffeine and alcohol. The function of gastrin is to stimulate gastric acid production, pepsin secretion, gastric motility and the growth of gastric mucosa. Negative feedback regulates secretion at pH 2.5, with maximal suppression at pH 1.0, to safe- guard against over-acidification. Gastric pH Concurrent Tests Gut hormones (if symptoms include flushing and/or diarrhoea) Fasting sample required (at least 10 hours). Withhold proton pump inhibitors (e.g. omeprazole) for 2 weeks. If a gastrinoma is suspected it is at the clinician's discretion whether or not to take the Dietary Requirements patient off H2 antagonist treatment before testing. If a fasting sample shows a borderline or high level, it may be necessary to cease medication for 72 hour before repeating the screen. In normal patients who are properly fasted and off medications that suppress gastric acid production: normal gastrin = 10-90 ng/L

Moderately elevated gastrin levels are seen patients with pernicious anemia, pyloric stenosis, chronic atrophic gastritis, vagotomy without gastric resection, short bowel syndrome, chronic renal failure, and hyperparathyroidism, and with H2 receptor antagonist or steroid therapy. Postprandial levels seldom exceed 250 ng/L. Interpretation

Proton pump inhibitors inhibit gastric acid secretion, resulting in gastrin levels as high as 1000 ng/L.

The commonest cause of high gastrin levels, even in active duodenal ulcer subjects, is a slight degree of gastritis and relative hypochlorhydria. Any duodenal ulcer patient with a raised gastrin (not due to renal failure) should have gastric secretory studies even

Version 1.0 Date: 21/06/12 Document agreed by: Dr Lisa Bailey though it is recognised that this may be both difficult to arrange and unpleasant for the patient. Gastrin > 1000 ng/L with gastric pH < 2.5 is diagnostic of gastrinoma. However, 60% of patients with ZE syndrome have gastrin levels that are elevated but less than 1000 ng/L. In these cases a secretin provocative test is helpful.

High gastrin levels can also be seen in achlorhydria, an autoimmune disease of acid-secreting cells causing failure of acid secretion, due to loss of feedback of acid on gastrin secretion. Collection Conditions Collect sample onto ice and send immediately to lab. Frequency of testing As required, contact lab for urgent analysis.

Version 1.0 Date: 21/06/12 Document agreed by: Dr Lisa Bailey