Application value of CaNO and FeNO combined with lung function in diagnosis of bronchial asthma

  Background   Concentration of alveolar nitric oxide (CaNO) and fractional exhaled nitro oxide (FeNO) are noninvasive indicators of small airway inflammation in alveolar acinar area and primary airway inflammation in large airway in asthma, respectively. The Guidelines of the National Institute for Health and Clinical Excellence (NICE) in the United Kingdom recommend FeNO combined with other asthma adjuvant tests as a reference indicator for the diagnosis of asthma. As an inflammatory marker of small airways, CaNO has not been studied in the diagnosis and treatment of asthma. The combined assessment of small and large airway inflammation can comprehensively reflect the level of airway inflammation, which can overcome the shortcomings of a single test.

  Objective   To investigate the value of CaNO and FeNO combined with lung function parameters in the diagnosis of asthma.

  Methods   A retrospective analysis was conducted on 66 asthma patients treated in the Department of Respiratory of the First Medical Center, Chinese PLA General Hospital from March to September in 2019, and the patients were included as asthma group, another 37 non-asthmatic patients with cough and shortness of breath during the same period as control group. The general data, CaNO, FeNO, pulmonary function parameters were compared between the two groups, and ROC curve was used to detect the value of CaNO or FeNO alone and combined lung function in the diagnosis of asthma.

  Results   There was no statistical difference in general data between the two groups (P>0.05). CaNO level and FeNO level in the asthma group were higher than those in the control group, and the levels of lung function parameters FEV1%, FVC%, FEV1/FVC%, MMEF%, FEF75% and FEF50% were lower than those in the control group (P<0.05). The critical value for CaNO diagnosis of asthma was 3.45 × 10⁹ mol/L, at which the sensitivity, specificity and area under ROC curve were 72.7%, 86.5% and 0.872 (95% CI 0.804-0.941), respectively. The critical value of FeNO for the diagnosis of asthma was 30.5 × 10⁹ mol/L, with sensitivity of 62.1%, specificity of 83.8%, area under ROC curve of 0.770 (95% CI 0.679-0.860). The diagnostic value of CaNO and FeNO combined with FEV1%, FVC%, MMEF% and FEF50% was higher than that of CaNO or FeNO alone, and the area under the curve of CaNO + FeNO + FEV1 was the largest, which was 0.954 (95% CI 0.915-0.993), with sensitivity of 93.9%, specificity of 86.5%, and the positive likelihood ratio of CaNO + FeNO + FEF50 was the highest (31.407), the negative likelihood ratio was 0.156, and the area under the curve was 0.952 (95% CI 0.912-0.992).

  Conclusion   CaNO and FeNO combined with lung function test can be used as a supplementary tool for asthma diagnosis.