GAST and Zollinger-Ellison syndrome: An NIH study of a large number of NIH ZES patients and ZES patients undergoing secretin testing in the literature (i.e., >500) [229] reported that the best criterion for a positive test in ZES patients was an increase in serum gastrin with secretin ≥ 120 pg/mL, which had a sensitivity of 94% and specificity of 100% for identifying ZES patients [229].