CGA and Zollinger-Ellison syndrome: Furthermore, its low specificity is particularly a problem with suspected ZES patients because of the presence of tumor-induced hypergastrinemia causing gastric ECL hyperplasia in the actual ZES patients, resulting in an increased CgA level not being an expression of only a possible gastrinoma as well as the fact that the use of PPIs also resulting in ECL hyperplasia in non-ZES patients results in a possible false positive ZES/pNET/NET diagnosis.