ABC Classification Is Less Useful for Older Koreans Born before 1960

Background/Aims: In the ABC classification system, group A consists of seronegative subjects without gastric corpus atrophy. This study aimed to determine the prevalence and characteristics of pseudo group A subjects. Methods: Group A subjects were identified among consecutive Korean adults who underwent a serum anti-Helicobacter pylori immunoglobulin G (IgG) test and pepsinogen (PG) assay on the day of endoscopy. Past infection was defined as the presence of either eradication history or endoscopic findings suggesting past infection (i.e., gastric xanthoma, metaplastic gastritis, or advanced atrophy >closed-type 1). Results: Among 2,620 group A subjects, 448 (17.1%) had eradication history, and 133 (5.1%) showed endoscopic findings suggesting past infection. Older age (odds ratio [OR], 1.148; 95% confidence interval [CI], 1.067 to 1.236) and earlier year of birth (OR, 1.086; 95% CI, 1.009 to 1.168) were independent risk factors for classification into pseudo group A, with cutoff points at 50.5 years and birth year of 1959.5, respectively. Positive H. pylori test findings were found in 22 subjects (3.1%) among the 715 subjects who underwent the urea breath test or Giemsa staining on the same day. Current infection was positively correlated with PG I and PG II levels (p