Defining the normal range of fractional exhaled nitric oxide in children: one size does not fit all

Use of exhaled nitric oxide in the diagnosis and monitoring of childhood asthma: myth or maxim?

Asthma is a common condition in children. This review describes the evidence from the literature and international asthma guidelines for using fractional exhaled nitric oxide (FENO) in the diagnosis and monitoring of childhood asthma. The accuracy of FENO measuring devices could be further improved, the difference in FENO results between devices are equivalent to what is considered a clinically important difference. For diagnosing asthma no guideline currently recommends FENO is used as the first test, but many recommend FENO as part of a series of tests. A cut-off of 35 ppb is widely recommended as being supportive of an asthma diagnosis, but evidence from children at risk of asthma suggests that a lower threshold of 25 ppb may be more appropriate. Nine randomised clinical trials including 1885 children have added FENO to usual asthma care and find that exacerbations are reduced when care is guided by FENO (OR for exacerbation compared to usual care 0.77, 95% CI 0.62-0.94). What is not clear is what cut-off(s) of FENO should be used to trigger a change in treatment. After 30 years of intensive research there is not sufficient evidence to recommend FENO for routine diagnosing and monitoring asthma in children.

Educational aims

To give the reader an overview of literature that supports and does not support the role of FENO in diagnosing asthma in children.To give the reader an overview of literature that supports and does not support the role of FENO in monitoring asthma in children.To give the reader an understanding of the role of FENO in international guidelines for diagnosing and monitoring asthma in children.

Fractional exhaled nitric oxide in the assessment of exercise-induced bronchoconstriction: A multicenter retrospective analysis of UK-based athletes

INTRODUCTION

Exercise-induced bronchoconstriction (EIB) is not only highly prevalent in people with asthma, but can also occur independently, particularly in athletes. Fractional exhaled nitric oxide (FeNO) is an indirect biomarker of type 2 airway inflammation that has an established role in the assessment and management of asthma. The aim was to evaluate the value of FeNO in the assessment of EIB in athletes.

METHOD

Multicenter retrospective analysis. In total, 488 athletes (male: 76%) performed baseline FeNO, and spirometry pre- and post-indirect bronchial provocation via eucapnic voluntary hyperpnea (EVH). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated for established FeNO thresholds-that is, intermediate (≥25 ppb) and high FeNO (≥40 ppb and ≥ 50 ppb)-and were evaluated against objective evidence of EIB (≥10% fall in FEV₁ ). The diagnostic accuracy of FeNO was calculated using receiver operating characteristics area under the curve (ROC-AUC).

RESULTS

Thirty-nine percent of the athletes had a post-EVH fall in FEV₁ consistent with EIB. FeNO values ≥25 ppb, ≥40 ppb, and ≥ 50 ppb were observed in 42%, 23%, and 17% of the cohort, respectively. The sensitivity of FeNO ≥25 ppb was 55%, which decreased to 37% and 27% at ≥40 ppb and ≥ 50 ppb, respectively. The specificity of FeNO ≥25 ppb, ≥40 ppb, and ≥ 50 ppb was 66%, 86%, and 89%, respectively. The ROC-AUC for FeNO was 0.656.

CONCLUSIONS

FeNO ≥40 ppb provides good specificity, that is, the ability to rule-in a diagnosis of EIB. However, due to the poor sensitivity and predictive values, FeNO should not be employed as a replacement for indirect bronchial provocation in athletes.