PP13 EVALUATING FENO (FRACTIONAL EXHALED NITRIC OXIDE) AND EOSINOPHIL LEVELS FOR PRECISE ASTHMA PHENOTYPING AMONG ASTHMATIC PATIENTS IN HOSPITAL SULTAN ABDUL AZIZ SHAH (HSAAS), UPM

Li Li Kwan¹, Ummi Nadira Daut², Tasnim Abdul Aziz²

¹Department of Internal Medicine, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia.
²Department of Internal Medicine, Hospital Sultan Abdul Aziz Shah, Universiti Putra Malaysia.

Introduction
Asthma is a heterogeneous disease characterized by variable airway inflammation, comprising phenotypes such as eosinophilic and non-eosinophilic asthma, which respond differently to therapy. Biomarkers like fractional exhaled nitric oxide (FeNO) and blood eosinophils are increasingly used for phenotyping to guide personalized therapy.

Objective
This study aims to evaluate the utility of FeNO and eosinophil levels in differentiating eosinophilic and non-eosinophilic asthma among patients at Hospital Sultan Abdul Aziz Shah (HSAAS), UPM.

Methodology
This prospective observational study recruited 70 adult asthmatic patients from HSAAS. Clinical, demographic, spirometry, FeNO, blood eosinophil counts, Asthma Control Test (ACT), and Test of Adherence to Inhalers (TAI) data were collected. Eosinophilic asthma was defined by blood eosinophils >300 cells/mm³. 

Results
The cohort had a median age of 39 years (range: 18-65) and was predominantly female (82.86%). Most patients used inhaled corticosteroid and long-acting beta-agonist (ICS/LABA) inhalers (68.57%), and a majority had allergic rhinitis (52.86%). Multiple linear regression analysis showed that for each 1 kg/m² increase in BMI, FeNO levels decreased by an average of 1.46 ppb (p=0.001). Additionally, patients without a history of other atopies or with a history of gastroesophageal reflux disease (GERD) had lower FeNO values. FeNO levels correlated positively with peripheral blood eosinophil levels (r=0.3966, p=0.0008). Receiving Operator Characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.65, confirming the utility of blood eosinophil levels to distinguish eosinophilic from non-eosinophilic asthma patients, with an optimal cut-off value at 41.00 ppb (sensitivity 54.29%, specificity 78.79%).

Conclusion
FeNO levels correlate with blood eosinophils and can effectively distinguish eosinophilic from non-eosinophilic asthma. However, BMI, atopy status, and GERD may also affect observed FeNO levels, potentially acting as confounders. Despite moderate sensitivity, FeNO remains a useful, non-invasive adjunct for asthma phenotyping, aiding precision in treatment planning when combined with clinical and laboratory markers.