[Relationship between FeNO levels and asthma severity: a cross-sectional study at the University Hospital of Puebla].

Introduction: The evaluation of patients with asthma uses clinical tools such as the Asthma Control Test (ACT), pulmonary function tests, and biomarkers. Among these, an elevated fractional exhaled nitric oxide (FeNO) level can predict a higher risk of exacerbations and response to corticosteroids and/or biological therapies, although it does not always reflect poor clinical control. Our objective was to determine the relationship between asthma severity and FeNO levels in patients attending our service.

Methods: A cross-sectional study was conducted in patients over 12 years of age with controlled asthma assessed by ACT. FeNO was measured using the NIOX-VERO^® device. Descriptive analysis and Spearmans correlation coefficient were applied.

Results: Thirty-six patients (66.7% women) with a mean age of 36.3 years (SD ± 14.4) were included. According to GINA, 63.9% had mild asthma and 36.1% had moderate asthma. 22.2% had low FeNO levels (<25 ppb) and 52.8% had high levels (>50 ppb). The mean FeNO level in mild asthma was 62.7 ppb (SD ± 62.7) and in moderate asthma, 54.8 ppb (SD ± 36.2). No significant correlation was found between asthma severity and FeNO levels (rs = 0.150, p = 0.306).

Conclusions: Although more than half of the patients had elevated FeNO levels, no significant association was observed with asthma severity. This finding is consistent with previous studies and suggests that FeNO, although useful as a biomarker of type 2 inflammation, should not be used in isolation to assess clinical severity.