Gastrinoma

Question: Which of the following tests would best differentiate the two conditions? 17: A 54-year-old man who has had a Billroth II procedure for peptic ulcer disease now presents with abdominal pain and is found to have recurrent ulcer disease. The physician is considering this patient’s illness to be secondary either to a retained antrum or to a gastrinoma. Which of the following tests would best differentiate the two conditions? a. Random gastrin level b. Determination of 24-h acid production c. Serum calcium level d. Secretin infusion

Answer: The diagnosis of gastrinoma requires the demonstration of fasting hypergastrinemia and an increased basal gastric acid output (BAO) (hyperchlorhydria). Nearly all patients with gastrinomas have fasting hypergastrinemia, although in 40 to 60% the level may be elevated by less than a factor of 10. Therefore, when the diagnosis is suspected a fasting gastrin level should be determined first. Potent gastric acid–suppressant drugs such as proton pump inhibitors (omeprazole, pantoprazole, lansoprazole, rabeprazole) can suppress acid secretion sufficiently to cause hypergastrinemia; because of their prolonged duration of action, these drugs need to be discontinued for a week before the gastrin determination. If the gastrin level is elevated, gastric pH should be measured. If gastric pH < 2.0, the hypergastrinemia is not a physiologic response to achlorhydria (atrophic gastritis, pernicious anemia), another common cause of hypergastrinemia. If the fasting gastrin > 1000 ng/L (10 times increased) and the pH < 2.0, which occurs in 40 to 60% of patients with gastrinoma, the diagnosis is established after ruling out the possibility of retained antrum syndrome by history. In patients with hypergastrinemia with fasting gastrin < 1000 ng/L and gastric pH < 2.0, other conditions such as H. pylori infections, antral G cell hyperplasia/hyperfunction, gastric outlet obstruction, or, rarely, renal failure can masquerade as a gastrinoma. To establish the diagnosis in this group, a determination of BAO and a secretin provocative test should be done. In patients with gastrinomas, BAO is usually (>80%) elevated (i.e., >15 meq/h) and the secretin provocative test is positive (i.e., >200 ng/L increase in serum gastrin level. Did you get it?