Download Gastrin

Gastrin
Description
A peptide hormone secreted by the G cells of the gastric antral
mucosa.
Indication
Diagnosis of gastrinoma in patients with gastric acid hypersecretion,
for example in Zollinger-Ellison (ZE) syndrome. May also be helpful
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.
Additional Info
Gastrin is secreted physiologically in response to several stimuli,
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 safeguard against over-acidification.
Concurrent Tests
Gastric pH
Gut hormones (if symptoms include flushing and/or diarrhoea)
Dietary Requirements
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
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
Interpretation
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.
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
Document agreed by: Dr Lisa Bailey
Date: 21/06/12
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
Document agreed by: Dr Lisa Bailey
Date: 21/06/12