Background Fractional exhaled nitric oxide (FeNO) is a non-invasive biomarker for airway eosinophilic inflammation. However, the clinical value of ultrahigh FeNO (≥100 parts per billion (ppb)) in predicting asthma is never explored. We aimed to investigate the value of ultrahigh FeNO as a predictor of bronchial hyperresponsiveness (BHR), an important index for asthma diagnosis.
Methods A retrospective cohort study was conducted on 259 patients with suspected asthma who received the examination of FeNO, spirometry, bronchial provocation test (BPT) and differential cell count of induced sputum. Patients were stratified by FeNO value: ultrahigh (group A:≥100 ppb), high (group B: 50–99 ppb), intermediate (group C: 26–49 ppb) and normal (group D:≤25 ppb). The positive rates of BPT and sputum eosinophils percentage (Eos%) were compared among four cohorts. The correlations between FeNO and sputum Eos% were measured.
Results A significant higher positive rate of BPT was observed in group A (90.91%) than all others (B: 51.43%, C: 31.43%, D: 28.13%, all p<0.01). Referring to group D, the ORs of positive BPT in groups A, B and C were 26.84, 2.84 and 1.05. Sputum Eos% in group A (19.75 (7.00, 46.25)) is higher than that in others (B: 3.50 (1.00, 12.75), C: 1.13 (0.06,3.50), D: 0.50 (0.00, 2.13)). FeNO correlates with sputum Eos% in groups A and B, but not group C or D.
Conclusions Ultrahigh FeNO correlates with BHR and could serve as a practical alternative to methacholine challenge to support an asthma diagnosis in patients with suspected asthma in primary care.
- fractional exhaled nitric oxide
- bronchial hyperresponsiveness
- eosinophilic inflammation
- primary care
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Contributors Study concept and design: RC and WC. Data acquisition: JL, RX and CZ. Data analysis: JL, WL, RC and WC. JL, RX and CZ wrote the first draft of the paper, which was then critically reviewed by RC, WC, KL and NZ. All authors read and approved the final manuscript.
Funding This research was partly supported by grants from Incubative Project for Innovation Team of Guangzhou Medical University (2017-159), State Key Laboratory of Respiratory Disease (SKLRD-QN-201702) and National Natural Science Foundation of China (81870079).
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The study was approved by the Ethics Committee of the First Affiliated Hospital of Guangzhou Medical University (No. IRB 2016-52).
Provenance and peer review Not commissioned; externally peer reviewed.
Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information.
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