Background: Enzyme-linked immunosorbent assay (ELISA) is the most commonly used serologic test for Helicobacter pylori. This study aimed to investigate the effects of age and atrophic gastritis on the diagnostic accuracy of an immunoglobulin G (IgG) antibody test against H. pylori in adults. Methods: One hundred and seventy dyspeptic patients (age range, 20-70 years) were evaluated. H. pylori infection was diagnosed when culture or both urease and histological tests were positive. Serum pepsinogen-I (P-I) and pepsinogen-II (P-II) levels were measured. Atrophic gastritis was defined when P-I ≤ 70 μg/L and P-I/P-II ≤ 3. A quantitative ELISA test (HEL-pTEST II) was used for IgG antibodies against H. pylori. Results: The H. pylori prevalence rate was 62.1%. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of ELISA were 93.5%, 94.4%, 95.6%, 91.9%, and 93.9% in patients aged < 45 years, and 100%, 81.3%, 94.3%, 100%, and 95.6% in patients aged ≥ 45 years, respectively. Twenty-six patients had atrophic gastritis. There was 100% sensitivity and 86.7% specificity in atrophic gastritis and 96.5% sensitivity and 91.9% specificity in non-atrophic gastritis. Conclusion: The quantitative ELISA test is a good noninvasive test even in older age groups and is a suitable test in patients with atrophic gastritis due to its excellent sensitivity.