FeNO testing in severe asthma: A clinical argument or an access constraint?

Fractional exhaled nitric oxide in a respiratory healthy general population through the lifespan

INTRODUCTION AND OBJECTIVES

The fractional exhaled fraction of nitric oxide (FeNO) is used in clinical practice for asthma diagnosis, phenotyping, and therapeutic management. Therefore, accurate thresholds are crucial. The normal FeNO values over lifespan in a respiratory healthy population and the factors related to them remain unclear.

MATERIALS AND METHODS

We determined FeNO levels in 2,251 respiratory healthy, non-atopic, and non-smoking participants from the Lung, hEart, sociAl, boDy (LEAD) cohort, a general population, observational cohort study of participants aged 6-82 years in Austria.

RESULTS

The median FeNO value in the total study population was 13.0 [interquartile range: 9.0, 20.0] ppb, increases with age, and, except in young participants (<18 years: 9.0 [7.0, 12.0], ≥18 years: 15.0 [11.0, 22.0]), it was significantly lower in females versus males. Multiple regression analyses showed that body height and blood eosinophil counts were associated with higher FeNO levels, both in children/adolescents and adults. In children/adolescents, FeNO values were positively associated with total IgE levels, FEV1/FVC ratio, and urban living. In adults, FeNO was positively associated with age and negatively associated with the presence of cardiovascular and ischaemic vascular disease.

CONCLUSIONS

We identified the normal FeNO ranges within a respiratory healthy population at different age ranges and associated factors. Collectively, they serve as a reference to frame FeNO values in clinical practice.

German Asthma Net: Characterisation of responders to anti-IL-5 and anti-IL-5(R) therapy

INTRODUCTION

Previous studies of anti-IL-5/IL-5(R) therapies in severe asthma found that response was mainly predicted by indicators of good baseline disease control. However, long-term response predictors remain unclear.

METHODS

Responders to anti-IL-5/IL-5(R) therapy in the well-characterised, real-life, international German Asthma Net (GAN) registry were analysed using regression analyses. Response was defined by ≥50% reduction in exacerbations or corticosteroid dose, super-response by a complete stop of both, and remission additionally by controlled asthma (ACT score≥20).

RESULTS

Seventy-seven percent of 347 patients (55% female, 56.6±12.3 years, follow-up 20.3±13 months) were responders and showed improved exacerbation rates, asthma control, and corticosteroid treatment reduction. Response was independently predicted by inhaled corticosteroid dose (odds ratio [OR] 1.5; p = 0.014), exacerbation rate (OR 1.2; p = 0.009), and treatment duration (OR 1.05, p = 0.023). Univariately, blood eosinophil counts notably predicted response (OR 12.4; p = 0.004). Super-response was inversely associated with corticosteroid dependence and depression. Remission was associated with the absence of systemic corticosteroids, better asthma control, and FEV1 in litre.

CONCLUSIONS

These results underscore that long-term anti-IL-5/IL-5(R) therapy reduces exacerbation and corticosteroid burden, especially in patients with severe disease and high type 2 inflammatory burden. Contrastingly, low baseline corticosteroid use and markers of good asthma control predicted remission and super-responder status.

Comparison of usability and user-friendliness of three FeNO analyzers in a general population cohort of the LEAD study

Exhaled nitric oxide (FeNO) is a marker for airway inflammation measured by hand-held or stationary analyzers, but their usability was not previously assessed. NIOX VERO (CN), NObreath (BN), Vivatmo pro (BV), and CLD88 analyzer (reference, EC) were compared in a prospective study of the general population LEAD (Lung, hEart, sociAl, boDy) cohort, including the System Usability Scale and tests for equivalence at a clinically relevant range of ≤ 70 ppb with linear models and Bland-Altman plots. In 486 participants (62.4 ± 14.2 years old, 48.1% female), all hand-held analyzers had a good usability score, with BN scoring best. BV required the fewest attempts and time to measurement success, followed by BN. The FeNO results were clinically equivalent between devices (difference to EC 0.7-7.5 ppb) with increasing variability at higher FeNO values. The analyzers had an agreement of ≥ 95% at the threshold of ≥ 40 ppb. CN showed the lowest difference to EC, followed by BV. All portable analyzers showed good usability with an above-average usability score. The best usability score was observed with the BN device, while the BV device had the shortest measuring time and the fewest additional attempts. The lowest difference to the stationary EC analyzers was observed with the CN device.

What is the added value of FeNO as T2 biomarker?

There is increasing evidence about the role of nitric oxide in type 2 (T2) immune response. Fraction of exhaled nitric oxide (FeNO) is a product of airways inflammation and it is increased in patients with asthma. Since Gustaffson published the first article about this biomarker in the 1990s, interest has continued to grow. Compared with other T2 biomarkers such as blood eosinophil count, induced sputum, or serum periostin, FeNO has some remarkable advantages, including its not invasive nature, easy repeatability, and possibility to be performed even in patients with severe airway obstruction. It is considered as an indicator of T2 inflammation and, by the same token, a useful predictor for inhaled steroid response. It is difficult to determine the utility of nitric oxide (NO) for initial asthma diagnosis. In such a heterogenous disease, a single parameter would probably not be enough to provide a complete picture. There is also an important variability among authors concerning FeNO cutoff values and the percentage of sensibility and specificity for diagnosis. Its high specificity indicates a potential role to “rule in” asthma; however, its lower sensibility could suggest a lower capacity to “rule out” this pathology. For this reason, if a diagnosis of asthma is being considered, FeNO should be considered along with other tests. FeNO has also shown its utility to detect response to steroids, adherence to treatment, and risk of exacerbation. Even though there is not enough quality of evidence to establish overall conclusions, FeNO could be an alternative procedure to diagnose or exclude asthma and also a predictive tool in asthma treated with corticosteroids.