On the basis of the levels of serum pepsinogen I (S-PGI) and gastrin-17 (S-G-17) as well as Helicobacter pylori - antibodies assayed from a blood sample it is possible to establish with high sensitivity and specificity whether the patient has gastritis, whether the gastritis is atrophic or not and in which part of the stomach the atrophic changes are located. The test enables the identification of patients whose risk of gastric cancer, of the consequences of vitamin B12 deficiency (e.g. elevated levels of homocysteine) or of peptic ulcer is considerably increased and who can then undergo gastroscopy. It also facilitates the diagnosis of non-atrophic Helicobacter gastritis enabling treatment before endoscopy.