S100A9 and pulmonary arterial hypertension: Subsequent evaluation of the diagnostic value of S100A9 in PAH revealed an impressive AUC of 0.931 (95% CI = 0.832–0.981) in GSE117621 and an AUC of 0.722 (95% CI = 0.457–0.907) in GSE4819, underscoring the significance of S100A9 in PAH diagnosis.108