In the training cohort, the AUC was 0.9981 (95% CI, 0.993–1), while in the testing cohort, the AUC was 0.862 (95% CI, 0.7271–1), indicating the diagnostic value of S100A9 for AF and S100A9 is identifying as a potential AF biomarker.133. This evidence concerns the gene S100A9 and atrial fibrillation.