Before the use of potent acid suppressing drugs and in particular proton pump inhibiters (PPI), most patients with gastrinoma presented with ZollingerEllison syndrome and diagnosis was problematic in only a few. In recent years, the syndrome is rarely seen and gastrinoma patients present with less overt symptoms and hypergastrinaemia which may be mild. Increasingly patients present later.
In the population, hypergastrinaemia most commonly occurs because of stimulation of antral G cells generally due to the lack of negative feed back when gastric acid is absent. In the diagnostic laboratory hypergastrinaemia is frequently recorded due to; post-prandial specimen collection at clinics, H-pylori infection, acid suppressing drug administration, atrophic gastritis and less frequently with impaired renal function, or gastrinoma.
Chromogranin A (CgA) is the best general marker for endocrine tumours and is raised in the circulation of patients with gastrinoma. However, CgA is also raised when gastric acid is absent.
In a tertiary referral laboratory for the diagnosis of endocrine tumours of gastoenteropancreatic origin we have studied requests for gastrin and chromogranin A assay in patients under investigation for gastrinoma (N=500).
Chromogranin A is raised in 46% of these patients. Five percent were gastrinomas. The remaining patients had unsuspected endocrine tumours other than gastrinoma (frequently serotonin producing tumours of the ileum or colon), atrophic gastritis, were on PPI therapy or had no known relevant diagnosis.
Gastrin was raised in 28% of patients 5% being gastrinoma.
We have also studied gastrin in several groups of subjects (N=2550), normal healthy controls with or without H-pylori infection and patients with duodenal ulcer during and after PPI therapy, autoimmune atrophic gastritis, idiopathic achlorhydria, renal failure and gastrinoma and compared circulating gastrin both fasting and post-prandially in these groups using three regional specific antisera. This has illustrated that gastrinoma remains a difficult laboratory diagnosis in many patients.