Control maintenance can be predicted by exhaled NO monitoring in asthmatic patients

Fractional exhaled nitric oxide as a determinant for the clinical course of asthma: a systematic review

Background: Precision medicine means linking the right patient to the right management strategy including best possible pharmacological therapy, considering the individual variability of the disease characteristics, type of inflammation, genes, environment, and lifestyle. For heterogenous diseases such as asthma, reliable biomarkers are needed to facilitate the best possible disease control and reduce the risk of side effects. The present review examines fractional exhaled nitric oxide (FeNO) as a guide for the management strategy of asthma and predictor of its clinical course.

Method: The literature included was identified by searching the PubMed database using specific key words and MeSH terms. Studies were not excluded based on their design alone. The search resulted in 212 hits, of which 35 articles were included in this review.

Results: Several studies support a potential role for high FeNO levels as a prognostic biomarker for accelerated lung function decline in adults with newly diagnosed asthma. Furthermore, studies report an association between high FeNO levels and excess decline in FEV₁ in adults with long-standing moderate to severe asthma despite optimised therapy, whereas the findings for patients with less severe disease are conflicting. Applying a FeNO-based management algorithm reduces the exacerbation rate in adults with asthma. Similar observations are seen in children, though based on fewer studies. The available studies provide evidence that the level of FeNO may be useful as a predictor of subsequent loss of asthma control in adults, though the evidence is somewhat conflicting in children and young adults.

Conclusion: The present review provides evidence of the prognostic value of FeNO as a surrogate biomarker for type 2 inflammation in the airways. FeNO is likely to emerge as an important biomarker in monitoring and tailoring modern asthma treatment, either alone or in combination with other biomarkers.

Correlations between exhaled nitric oxide, rs28364072 polymorphism of FCER2 gene, asthma control, and inhaled corticosteroid responsiveness in children with asthma

In children with asthma, the responsiveness of inhaled corticosteroids (ICS) is depended on asthma endotype and phenotype. This study aimed to describe the clinical and biological characteristics, and its correlation with polymorphism of rs28364072 in FCER2 of asthmatic children. This work aimed to study the correlation between fractional concentration of exhaled nitric oxide (FE_NO) level and rs28364072 polymorphism of FCER2 gene with ICS responsiveness and disease control in children with asthma. This study was a prospective and descriptive study. All clinical characteristics, FE_NO, blood eosinophil counts (BEC), skin prick test (SPT), total IgE, asthma control test, and FCER2 gene polymorphism were performed for each patient. One hundred and seven asthmatic children who were over 5 years old (9.2 ± 2.6), were included. Patients with FE_NO > 20 ppb had higher percentage of positive SPT, total IgE level, and BEC (89.2 vs 80.0%, 851.1 vs 656.9 UI ml^-1, and 785 ± 576 G L^-1 vs 425 ± 364 G L^-1; respectively). Among them, there were 54.2% of homozygous TT, 36.4% of heterozygous TC, and 9.4% of homozygous CC of rs28364072 polymorphism in FCER2. The percentage of patients with controlled asthma was increasing after 1 month and 3 months (47.1% and 58.8%; respectively). During the study, the ICS was decreasing as indicated by asthma control (348 ± 118 mcg at 1st month vs 329 ± 119 mcg at 3rd month; p < 0.05). CC genotype had the lowest level of increasing FEV1 compared to that in genotype TC and TT (8.4% vs 8.7% and 27.1%; p > 0.05 and p < 0.05; respectively). The percentage of polymorphism in rs28364072 of FCER2 was significant higher in patients with controlled asthma compared to uncontrolled asthma. Asthmatic children with high FE_NO and rs28364072 polymorphism in FCER2 gene are good responders to ICS; however, asthmatic children with homozygous variant CC of rs28364072 are poorly responsive to ICS.

Type 2-high asthma is associated with a specific indoor mycobiome and microbiome

Background

The links between microbial environmental exposures and asthma are well documented, but no study has combined deep sequencing results from pulmonary and indoor microbiomes of patients with asthma with spirometry, clinical, and endotype parameters.

Objective

The goal of this study was to investigate the links between indoor microbial exposures and pulmonary microbial communities and to document the role of microbial exposures on inflammatory and clinical outcomes of patients with severe asthma (SA).

Methods

A total of 55 patients with SA from the national Cohort of Bronchial Obstruction and Asthma cohort were enrolled for analyzing their indoor microbial flora through the use of electrostatic dust collectors (EDCs). Among these patients, 22 were able to produce sputum during “stable” or pulmonary “exacerbation” periods and had complete pairs of EDC and sputum samples, both collected and analyzed. We used amplicon targeted metagenomics to compare microbial communities from EDC and sputum samples of patients according to type 2 (T2)-asthma endotypes.

Results

Compared with patients with T2-low SA, patients with T2-high SA exhibited an increase in bacterial α-diversity and a decrease in fungal α-diversity of their indoor microbial florae, the latter being significantly correlated with fraction of exhaled nitric oxide levels. The β-diversity of the EDC mycobiome clustered significantly according to T2 endotypes. Moreover, the proportion of fungal taxa in common between the sputum and EDC samples was significantly higher when patients exhibited acute exacerbation.

Conclusion

These results illustrated, for the first time, a potential association between the indoor mycobiome and clinical features of patients with SA, which should renew interest in deciphering the interactions between indoor environment, fungi, and host in asthma.

Study of the role of exhaled nitric oxide (NO) in predicting controlled or uncontrolled asthma in asthmatic children

Background

Exhaled nitric oxide (NO), especially fractional concentration of exhaled NO (FE_NO) has been used to predict the responsiveness to inhaled corticosteroid (ICS) in children with asthma. However, the use of exhaled NO for predicting asthma control in children is still controversial.

Methods

This was a perspective observational study. Asthmatic children who were naïve to inhaled corticosteroid (ICS) were included in the present study. The measurements of FE_NO and CA_NO (concentration of NO in the gas phase of the alveolar), spirometry, blood eosinophil counts (BEC), and total IgE levels were done for each asthmatic child. All study subjects started proper asthma treatment after the enrollment.

Results

Ninety three asthmatic children (9±3 years) with moderate (63.4%) to severe (36.6%) asthma were included and finished the 3-month study. The levels of FE_NO and CA_NO at inclusion were 37±11 ppb and 5.8±1.4 ppb, respectively; the mean of BEC was 617±258 cells/μL; the level of total IgE was 1563±576 UI/mL; 89% of subjects were positive for at least one respiratory allergen. The percentage of severe asthma was reduced significantly after 3 months (P<0.001). Well controlled asthma subjects at 3 months had higher levels of FE_NO and lower levels of CA_NO at inclusion (P<0.05 and P<0.05). FE_NO<20 ppb or CA_NO>5ppb had a risk of uncontrolled asthma at 3 months (OR: 1.7, CI 95% [(0.8) - (3.3)], P<0.05; OR: 1.9, CI 95% [(0.9) - (2.7)], P<0.05; respectively). FE_NO>35 ppb at inclusion had a positive predictive value for asthma control at 3 months (OR: 3.5, CI 95% [2.2-5.9], P<0.01).

Conclusions

Exhaled NO is a biomarker of asthma which may have a potential role to predict the control of asthma in short-term follow up in asthmatic children.

The influence of apocynin, lipoic acid and probiotics on antioxidant enzyme levels in the pulmonary tissues of obese asthmatic mice

Bronchial asthma and obesity are common health problems. Obesity is already responsible for 300,000 deaths per year.

AIMS

The aim of the present study was to assess whether apocynin, alpha lipoic acid and probiotic administration in combination with low-fat diet supplementation influences the levels of antioxidant enzymes in the pulmonary tissues of obese asthmatic mice.

MAIN METHODS

The study was performed on male C57/BL6 mice divided into 10 groups: (I) control; (II) asthma; (III) obesity; (IV) asthma + obesity; (V) asthma + obesity + apocynin p.o. 15 mg/kg/day for 12 weeks; (VI) asthma + obesity + low-fat diet for 12 weeks; (VII) asthma + obesity + low-fat diet for 12 weeks with apocynin p.o. 15 mg/kg/day; (VIII) asthma + obesity + low-fat diet with probiotics for 12 weeks; (IX) asthma + obesity + low-fat diet for 12 weeks with lipoic acid p.o. 100 mg/kg/day for 12 weeks; (X) asthma + obesity + standard diet with probiotics for 12 weeks. Superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GR) activity were examined. The administration of apocynin alone and apocynin in combination with a low-fat diet resulted in a significant increase in SOD values (respectively p < 0.001; p = 0.010). Application of probiotics resulted in a decrease in CAT activity (p = 0.037) and an increase in GPx activity (p < 0.001) compared to obese asthmatic mice. The administration of lipoic acid resulted in an increase in GR activity (p = 0.024 vs. control).

KEY FINDINGS

Supplementation containing apocynin, lipoic acid and probiotics has a positive influence on the antioxidant capacity of the pulmonary tissues of obese asthmatic mice.

SIGNIFICANCE

These results may contribute to the development of new therapeutic approaches.

The participation of oxidative stress in the pathogenesis of bronchial asthma

Reactive oxygen species are produced during oxygen reduction and are characterized by high reactivity. They participate in many important physiological processes, but if produced in high concentrations they lead to oxidative stress development and disturb pro-oxidative/anti-oxidative balance towards the oxidation reaction - leading to damage of lipids, proteins, carbohydrates or nucleic acids. Asthma is a chronic inflammatory disease of the airways of various pathogenesis and clinical symptoms, prevalence in recent years has increased significantly. Recently published literature point out the involvement of reactive oxygen species in the pathogenesis of asthma. Changes in the protein and lipid oxidation lead, among others, to pathological changes in the respiratory epithelial cells, an increase in vascular permeability, mucus overproduction, smooth muscle contraction or airway hyperresponsiveness (AHR). The aim of this study is to present the current state of knowledge on the influence of oxidative stress parameters on asthma development.

Fractional Exhaled Nitric Oxide for Identification of Uncontrolled Asthma in Children

OBJECTIVE

To determine the utility of Fractional Exhaled Nitric Oxide (FENO) in the identification of uncontrolled asthma in children on therapy, and to identify its cut-off value for determining asthma control.

METHODS

207 children (age 5-15 y) with physician-diagnosed asthma on therapy with at least 12 months follow up were enrolled. Spirometry and FENO measurements were performed. Asthma control was assessed as per GINA guidelines. Sensitivity and specificity of various cut-off values of FENO (15 ppb, 20 ppb, 25 ppb, 30 ppb) for identification of status of control of asthma were calculated.

RESULTS

156 (75%) children had uncontrolled or partly controlled asthma and 51 children were assessed to have controlled asthma. Median (IQR) FENO in children with controlled and uncontrolled asthma was 16 (11-23) ppb and 13 (11-25) ppb, respectively (P=0.26). No FENO cut-off had a reasonable combination of sensitivity and specificity to discriminate between controlled and uncontrolled asthma.

CONCLUSIONS

FENO, in itself, does not have good discriminatory value in assessment of controlled and uncontrolled asthma in children on asthma therapy.

Utilising exhaled nitric oxide information to enhance diagnosis and therapy of respiratory disease - current evidence for clinical practice and proposals to improve the methodology

INTRODUCTION

A non-invasive tool to diagnose respiratory diseases and to follow treatment has long been looked-for. Exhaled nitric oxide (NO) is a promising marker of inflammation in asthma but nearly 25-years of research has shown that it works in only certain endotypes of asthma. The modelling of NO dynamics of the lung can give more information than a single F_ENO value. Areas covered: The estimation of the NO production in the conducting airways and in the gas exchange area has given new insight of the NO production in diseases beyond asthma. In this article, we discuss the importance of methodology for NO measurement in the exhaled breath and the indication of applying this technique to detect respiratory disorders. This narrative review is an attempt to examine and discuss the physiological basis underlying exhaled NO measurements and the clinical evidence of the usefulness of this method in asthma and various other respiratory disorders. Expert commentary: Estimation of the NO parameters would aid in our understanding of the NO dynamics of the lung and thereby give more knowledge how to interpret the measured F_ENO value in clinical practice.

Fractional exhaled nitric oxide is a useful adjunctive modality for monitoring bronchial asthma

Background and Objective:

To evaluate the utility of fractional exhaled nitric oxide (FeNO) in monitoring asthma control.

Materials and Methods:

Steroid naïve nonsmoking asthmatics were recruited and followed for 6–8 weeks on standard treatment. Serial measurements of FeNO, peak expiratory flow rate (PEFR) variability, forced expiratory volume in 1 s (FEV1), bronchodilator reversibility (BDR), and asthma control test (ACT) score were measured at baseline and after 6–8 weeks of treatment.

Results:

One hundred and fifty-one patients were recruited over an 18-month period. These comprised 79 males (52.3%) with mean (standard deviation) age of 34.2 (11.6). Mean (SD) FeNO levels at baseline and after therapy were 45.4 (35.9) and 38.4 (23.7) ppb, respectively (P = 0.01). Baseline FeNO correlated strongly with FEV1 (r = −0.78, P < 0.001), ACT score (r = −0.76, P < 0.001), PEFR variability (r = −0.74, P < 0.001), and moderately with BDR (r = 0.50, P < 0.001). After treatment with inhaled steroids, the correlation remained strong with ACT score (r = −0.68, P < 0.001) but weakened with PEFR variability (r = −0.34, P = 0.01) and FEV1 (r = −0.36, P = 0.01).

Conclusions:

FeNO may be useful as an adjunctive noninvasive modality to assess asthma control in both steroid naïve asthmatics and asthmatics on treatment. However, the suboptimal sensitivity and specificity may limit its utility as a point-of-care single monitoring tool.

Predictive value of exhaled nitric oxide in the management of asthma: a systematic review

The clinical value of measuring fractional exhaled nitric oxide (FeNO) in asthma is not clear. We aimed to assess whether FeNO can reliably predict clinical outcomes in asthma treated with inhaled corticosteroids (ICS). We also evaluated whether its predictive role is influenced by different inflammatory phenotypes of asthma.

We conducted a systematic review focusing on five clinically relevant questions. Two authors independently screened search results, extracted data and assessed quality of the included studies. Data were synthesised by qualitative methods.

12 prospective studies were included, answering partly three of the five questions. In steroid-naïve asthma, a high FeNO level probably predicts good response to ICS. In ICS-treated asthmatics, a low FeNO level probably predicts low risk of exacerbation, and the patient is unlikely to benefit from increasing ICS dose. There were scarce data to conclude whether FeNO predicts exacerbations when ICS treatment is stopped in well-controlled asthma. Only one study reported results separately in different asthma phenotypes.

The current evidence on the predictive value of FeNO and its role in the management of asthma is incomplete. Future studies should focus on clinically meaningful questions and probably target only eosinophilic phenotypes where FeNO is best associated with the activity of airway inflammation.

Measurement of exhaled nitric oxide concentration in asthma: a systematic review and economic evaluation of NIOX MINO, NIOX VERO and NObreath

BACKGROUND

High fractions of exhaled nitric oxide (FeNO) in the breath of patients with symptoms of asthma are correlated with high levels of eosinophils and indicate that a patient is likely to respond to inhaled corticosteroids. This may have a role in the diagnosis and management of asthma.

OBJECTIVE

To assess the diagnostic accuracy, clinical effectiveness and cost-effectiveness of the hand-held electrochemical devices NIOX MINO(®) (Aerocrine, Solna, Sweden), NIOX VERO(®) (Aerocrine) and NObreath(®) (Bedfont Scientific, Maidstone, UK) for the diagnosis and management of asthma.

DATA SOURCES

Systematic searches were carried out between March 2013 and April 2013 from database inception. Databases searched included MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews, the Database of Abstracts of Reviews of Effects, Science Citation Index Expanded and Conference Proceedings Citation Index - Science. Trial registers such as ClinicalTrials.gov and the metaRegister of Controlled Trials were also searched in March 2013. All searches were updated in September 2013.

REVIEW METHODS

A rapid review was conducted to assess the equivalence of hand-held and chemiluminescent FeNO monitors. Systematic reviews of diagnostic accuracy and management efficacy were conducted. A systematic review of economic analyses was also conducted and two de novo health economic models were developed. All three reviews were undertaken according to robust high-quality methodology.

RESULTS

The rapid review (27 studies) found varying levels of agreement between monitors (Bland-Altman 95% limits of agreement up to ±10 parts per billion), with better agreement at lower FeNO values. Correlation was good (generally r > 0.9). The diagnostic accuracy review identified 22 studies in adults (all ages) and four in children. No studies used NObreath or NIOX VERO and seven used NIOX MINO. Estimates of diagnostic accuracy varied widely. FeNO used in combination with another test altered diagnostic accuracy only slightly. High levels of heterogeneity precluded meta-analysis. Limited observations included that FeNO may be more reliable and useful as a rule-in than as a rule-out test; lower cut-off values in children and in smokers may be appropriate; and FeNO may be less reliable in the elderly. The management review identified five randomised controlled trials in adults, one in pregnant asthmatics and seven in children. Despite clinical heterogeneity, exacerbation rates were lower in all studies but not generally statistically significantly so. Effects on inhaled corticosteroid (ICS) use were inconsistent, possibly because of differences in management protocols, differential effectiveness in adults and children and differences in population severity. One UK diagnostic model and one management model were identified. Aerocrine also submitted diagnostic and management models. All had significant limitations including short time horizons and the selective use of efficacy evidence. The de novo diagnostic model suggested that the expected difference in quality-adjusted life-year (QALY) gains between diagnostic options is likely to be very small. Airway hyper-responsiveness by methacholine challenge test is expected to produce the greatest QALY gain but with an expected incremental cost-effectiveness ratio (ICER) compared with FeNO (NObreath) in combination with bronchodilator reversibility of £1.125M per QALY gained. All remaining options are expected to be dominated. The de novo management model indicates that the ICER of guidelines plus FeNO monitoring using NObreath compared with guidelines alone in children is expected to be approximately £45,200 per QALY gained. Within the adult subgroup, FeNO monitoring using NObreath compared with guidelines alone is expected to have an ICER of approximately £2100 per QALY gained. The results are particularly sensitive to assumptions regarding changes in ICS use over time, the number of nurse visits for FeNO monitoring and duration of effect.

CONCLUSIONS

Limitations of the evidence base impose considerable uncertainty on all analyses. Equivalence of devices was assumed but not assured. Evidence for diagnosis is difficult to interpret in the context of inserting FeNO monitoring into a diagnostic pathway. Evidence for management is also inconclusive, but largely consistent with FeNO monitoring resulting in fewer exacerbations, with a small or zero reduction in ICS use in adults and a possible increased ICS use in children or patients with more severe asthma. It is unclear which specific management protocol is likely to be most effective. The economic analysis indicates that FeNO monitoring could have value in diagnostic and management settings. The diagnostic model indicates that FeNO monitoring plus bronchodilator reversibility dominates many other diagnostic tests. FeNO-guided management has the potential to be cost-effective, although this is largely dependent on the duration of effect. The conclusions drawn from both models require strong technical value judgements with respect to several aspects of the decision problem in which little or no empirical evidence exists. There are many potential directions for further work, including investigations into which management protocol is best and long-term follow-up in both diagnosis and management studies.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42013004149.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Contribution of exhaled nitric oxide measurement in airway inflammation assessment in asthma. A position paper from the French Speaking Respiratory Society

Nitric oxide (NO) is both a gas and a ubiquitous inter- and intracellular messenger with numerous physiological functions. As its synthesis is markedly increased during inflammatory processes, NO can be used as a surrogate marker of acute and/or chronic inflammation. It is possible to quantify fractional concentration of NO in exhaled breath (FENO) to detect airway inflammation, and thus improve the diagnosis of asthma by better characterizing asthmatic patients with eosinophilic bronchial inflammation, and eventually improve the management of targeted asthmatic patients. FENO measurement can therefore be viewed as a new, reproducible and easy to perform pulmonary function test. Measuring FENO is the only non-invasive pulmonary function test allowing (1) detecting, (2) quantifying and (3) monitoring changes in inflammatory processes during the course of various respiratory disorders, including corticosensitive asthma.

Asthma diagnosis and severity monitoring in primary school children: essential role of sequential testing of exhaled nitric oxide

BACKGROUND

Chronic eosinophilic airway inflammation, airflow limitation, and airway hyper-responsiveness are the mainstays of asthma diagnosis. The increased levels of exhaled nitric oxide (FeNO) in asthma are closely related to the extent of airway inflammation. Sequential measurement of FeNO concentrations may accurately predict asthma severity and guide therapeutic decisions.

METHODS

A total of 22,083 grade 1 students in Taipei city primary schools were screened for wheezing episodes using the International Study of Asthma and Allergies in Childhood questionnaire (ISAAC) questionnaires while their sero-atopic conditions were confirmed by Fluorescent Enzyme Immune Assay (FEIA). All students with allergies were tested by FeNO electrochemical test. 100 age-matched healthy students were used as control group (FeNO levels<25ppb).

RESULTS

From the 2650 students (12%) initially included via the wheezing criteria, 2065 (78.0%) were confirmed to have allergy by FEIA (sensitisation to at least two common aero-allergens in Taiwan) and diagnosed by a paediatric allergologist. Among them, 1852 (89.6%) had elevated FeNO values (>25ppb) and 266 (10%) had FeNO values<25ppb. Using the GINA guidelines, 140 mild-to-moderate asthma students who had received inhaled corticosteroids (ICS) with or without Singulair treatment completed serial FeNO testing every three months for one year. The FeNO levels decreased in 121 students (86.4%) and increased in 19 students (13.6%), which was compatible to changing childhood asthma control score and response to step-down treatment, respectively.

CONCLUSION

FeNO is an easy, used non-invasive tool for the diagnosis of allergic asthma. Sequential FeNO testing can accurately reflect asthma severity and provide for successful stepwise therapy for asthmatic children.

Impact of exhaled nitric oxide measurements on treatment decisions in an asthma specialty clinic

BACKGROUND

Asthma management in an outpatient setting is best accomplished by clinical evaluation coupled with spirometry and symptom evaluation, but these assessments do not provide information about airway inflammation. Exhaled nitric oxide (fraction of exhaled nitric oxide [FeNO]) measures T-helper cell type 2-mediated airway inflammation and may be a useful adjunct in asthma management.

OBJECTIVE

To determine whether the use of FeNO in the specialist management of asthma results in more effective and cost-effective treatment decisions.

METHODS

Fifty subjects 7 to 60 years old with established asthma participated in this observational study. Subjects were evaluated by clinical examination, spirometry, and symptom assessment using the Asthma Control Test, and clinicians estimated airway inflammation and made treatment decisions based on these assessments. Then, FeNO was measured, and changes in therapy based on FeNO levels were documented. The estimated cost impact of using FeNO was calculated presuming ongoing FeNO use in patient management.

RESULTS

Without FeNO, the clinician's assessment of airway inflammation was incorrectly classified in 50% of subjects. FeNO results substantially altered treatment decisions in more than one third of subjects, notably medication augmentation in 10 (20%) and medication decreases in 8 (16%). Use of FeNO in addition to standard of care was estimated to save $629 per subject per year.

CONCLUSION

Measurement of FeNO augments routine clinical assessment of asthma by measuring airway inflammation. Knowledge of FeNO affects medication treatment decisions to augment or decrease pharmacotherapy, which has important long-term asthma management implications, most notably the potential to lower the costs and morbidity associated with asthma exacerbation.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT01729247.

Clinical utility of asthma biomarkers: from bench to bedside

Asthma is a chronic disease characterized by airway inflammation, bronchial hyperresponsiveness, and recurrent episodes of reversible airway obstruction. The disease is very heterogeneous in onset, course, and response to treatment, and seems to encompass a broad collection of heterogeneous disease subtypes with different underlying pathophysiological mechanisms. There is a strong need for easily interpreted clinical biomarkers to assess the nature and severity of the disease. Currently available biomarkers for clinical practice - for example markers in bronchial lavage, bronchial biopsies, sputum, or fraction of exhaled nitric oxide (FeNO) - are limited due to invasiveness or lack of specificity. The assessment of markers in peripheral blood might be a good alternative to study airway inflammation more specifically, compared to FeNO, and in a less invasive manner, compared to bronchoalveolar lavage, biopsies, or sputum induction. In addition, promising novel biomarkers are discovered in the field of breath metabolomics (eg, volatile organic compounds) and (pharmaco)genomics. Biomarker research in asthma is increasingly shifting from the assessment of the value of single biomarkers to multidimensional approaches in which the clinical value of a combination of various markers is studied. This could eventually lead to the development of a clinically applicable algorithm composed of various markers and clinical features to phenotype asthma and improve diagnosis and asthma management.