Some patients with peptic ulcer disease will have mildly elevated serum gastrin levels. The gastrin stimulation test following secretin injection can help distinguish patients with gastrinoma and Zollinger-Ellison syndrome from patients with secondary causes for the elevated gastrin levels.
Patient selection: A patient with gastric acid hypersecretion and a high gastrin concentration (> 500 pg/mL, about 5 times the upper limit of normal) has Zollinger-Ellison Syndrome and does not need additional diagnostic testing.
Patient preparation: overnight fasting
Specimen: serum, separated immediately and frozen if immediately if testing delayed
dose of secretin to inject in units =
= (2-3 units) * (body weight in kilograms)
Method:
(1) Collect 2 fasting blood samples.
(2) Inject the secretin intravenously (IV) in 20-30 seconds.
(3) Collect samples at 2, 5, 10, 15, 20 and 30 minutes after the injection.
(4) Test all samples for gastrin.
basal fasting value in pg/mL =
= AVERAGE(2 fasting blood samples before secretin injection).
maximal increase in gastrin level in pg/mL after stimulation =
= (maximal value after secretin injection) - (basal fasting value prior to secretin)
Interpretation:
• A maximal increase >= 200 pg/mL is considered a "positive" test and is supportive for the diagnosis of Zollinger-Ellison Syndrome.
• An increase of 100 - 199 is considered suggestive (some consider positive).
• A few patients without gastrinomas may show increases up to 300 ng/mL.
• A normal person shows no increase or a mild decrease in gastrin levels.
