GAST and Atrophy: The ROC curve analysis results of the entire study population (N = 332) indicated that the diagnostic performance of advanced endoscopic atrophy (≥ O3 in the Kimura–Takemoto classification) and serology, including PG (PG I, ≤ 20.1 ng/mL; PG I/II ratio, ≤ 1.8) and gastrin (≥ 355 pg/mL), was high; therefore, they have sufficient diagnostic performance for use in daily clinical practice.