Fraction of exhaled nitric oxide (FeNO) is a potential noninvasive biomarker for assessing eosinophilic airway inflammation and guiding therapy adjustments. For a study published in Annals of Medicine, researchers evaluated the relationship between FeNO, serum eosinophil counts, spirometry measures, and symptom control among 82 asthma patients at a tertiary hospital’s asthma clinic. Results showed FeNO significantly correlated with serum eosinophil counts (r=0.450; P<0.001), asthma control test (ACT) scores (r=-0.648, P<0.001), and FEV₁ percentage predicted (r=-0.353; P=0.001). Higher FeNO levels were associated with poorly controlled asthma and a fivefold increased risk of abnormal FEV₁. The findings suggest FeNO, alongside ACT scores, could enhance asthma control rates by providing reliable markers of eosinophilic inflammation.