title: Usefulness of exhaled nitric oxide for diagnosing asthma.
abstract: BACKGROUND
  A standard asthma diagnosis is made based on clinical history, reversibility of airway obstruction, and bronchial hyperresponsiveness. Fractional exhaled nitric oxide (FeNO) is a noninvasive airway inflammatory marker that has been suggested as a diagnostic tool for asthma. The aim of this study was to establish a FeNO cut-off value for asthma diagnosis.
  
  
  METHODS
  One hundred and fourteen consecutive adult patients (mean age 34 ± 13 years) reporting symptoms consistent with asthma, with normal spirometric parameters and a negative bronchodilator test, were included in the study. All underwent a methacholine challenge test following the five-breath dosimeter protocol. FeNO was measured with a portable device (NioxMino, Aerocrine AB, Sweden) just before the methacholine challenge. The sensitivity, specificity, and diagnostic performance of FeNO measurement were calculated.
  
  
  RESULTS
  Thirty-five out of the 114 patients (30.7%) were diagnosed with asthma. A positive methacholine challenge was associated with higher FeNO levels and with lower forced expiratory volume in one second (FEV(1)) at baseline. No correlation was found between methacholine provocative concentration causing a decrease of 20% in FEV(1) (PC(20)) and FeNO levels. A receiver-operating characteristic curve was constructed for FeNO levels (area under the curve [AUC]: 0.762; 95% confidence interval [CI]: 0.667-0.857; p < .001). The FeNO cut-off point with maximal specificity and sensitivity for asthma diagnosis was 40 ppb.
  
  
  CONCLUSIONS
  Patients with confirmed asthma showed higher FeNO levels. A cut-off value of 40 ppb was calculated as the most efficient for asthma diagnosis in our population. The use of FeNO measurement may be a helpful tool to rule out a diagnosis of asthma, especially in patients in whom a methacholine challenge is not feasible or available.
authors: Department of Allergy, University Hospital La Paz, P. Castellana 261, Madrid, Spain. m.pedrosa.d@gmail.com
authors: María
authors: M
authors: Pedrosa
authors: Nataly
authors: N
authors: Cancelliere
authors: Pilar
authors: P
authors: Barranco
authors: Valentín
authors: V
authors: López-Carrasco
authors: Santiago
authors: S
authors: Quirce
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology; D001944:Breath Tests; D045853:Exhalation; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D009569:Nitric Oxide / Q000032:analysis*; D012372:ROC Curve
chemical_list: D009569:Nitric Oxide