Fractional exhaled nitric oxide and practical points in asthma diagnosis and management

Tuberk Toraks, cilt.74, sa.2, ss.106-120, 2026 (Hakemli Dergi)

Fractional exhaled nitric oxide and practical points in asthma diagnosis and

management

Asthma, a multifaceted chronic inflammatory disorder, concerns more than 300

million people worldwide. Recent developments have classified asthma into pre-

dominantly Type 2 (T2) high and T2 low categories. Specific biomarkers, more

so for T2 inflammation, determine the nature of inflammation. Fractional exhaled

nitric oxide (FeNO) has been presented as a reliable and non-invasive biomar-

ker of T2, eosinophilic, airway inflammation. The synthesis of nitric oxide (NO)

occurs through three isoforms of nitric oxide synthase (NOS), with inducible

NOS being predominantly expressed in inflammatory conditions, particularly in

response to cytokines like IL-4 and IL-13. Elevated FeNO levels have been related

to disease activity and have guided clinical decisions regarding corticosteroid

and biologic therapies. FeNO measurement has been found to be effective in

diagnosing asthma and assessing treatment response and adherence. The prac-

ticality of FeNO as a prognostic tool for exacerbation risk is highlighted in recent

studies. In particular, FeNO measurements may help establish individualized

treatment approaches and optimized treatment modalities, including biological

treatment based on inflammation profiles. However, despite its advantages, the

results of FeNO levels can be faked by many factors, such as genetics, environ-

mental conditions, and concomitant diseases. Considering all of these, it seems

helpful to integrate FeNO measurement into clinical practice in comprehensive

asthma management with cautious interpretation, thus improving patient out-

comes.

Key words: Asthma; nitric oxide; fractional exhaled nitric oxide; eosinophilic

inflammation