title: Nasal nitric oxide: longitudinal reproducibility and the effects of a nasal allergen challenge in patients with allergic rhinitis.
abstract: BACKGROUND
  Exhaled nitric oxide (eNO) is a validated noninvasive marker of airway inflammation in asthma. In patients with allergic rhinitis (AR), increased levels of nasal nitric oxide (nNO) have also been measured. However, the applicability of nNO as a marker of upper airway inflammation awaits validation.
  
  
  OBJECTIVE
  To test the longitudinal reproducibility of standardized nNO measurements in patients with AR and the effects of nasal allergen challenge.
  
  
  METHODS
  Twenty patients with clinically stable, untreated AR participated in a combined study design. First, reproducibility of nNO was tested over 1, 7, and 14-21 days. Subsequently, the effect of nasal allergen challenge on nNO was studied in a placebo-controlled, parallel design. Nasal NO was measured with a chemoluminescence analyzer. Ten subjects randomly underwent a standardized nasal allergen challenge; 10 subjects received placebo. Response to nasal challenge was monitored by composite symptom scores.
  
  
  RESULTS
  There was a good reproducibility of nNO up to 7 days [coefficient of variation (CV) over 1 (16.45%) and 7 days (21.5%)], decreasing over time [CV (14-21 days): 38.3%]. As compared with placebo, allergen challenge caused a significant increase in symptom scores (P < 0.001), accompanied by a decrease in nNO at 20 min postchallenge (P = 0.001). Furthermore, there was a gradual increase in nNO at 7 h, reaching significance at 24-h postallergen (P = 0.04).
  
  
  CONCLUSIONS
  Similar to eNO in asthma, nNO is a noninvasive marker, potentially suitable to monitor upper airway inflammation following allergen-induced late response. Present data show a good reproducibility of nNO measurements, decreasing over time, probably because of subclinical seasonal influences.
authors.affiliation: Centre for Human Drug Research, Leiden, The Netherlands.
authors.forename: J D
authors.initials: JD
authors.lastname: Boot
authors.forename: M L
authors.initials: ML
authors.lastname: de Kam
authors.forename: M A
authors.initials: MA
authors.lastname: Mascelli
authors.forename: B
authors.initials: B
authors.lastname: Miller
authors.forename: R Gerth
authors.initials: RG
authors.lastname: van Wijk
authors.forename: H
authors.initials: H
authors.lastname: de Groot
authors.forename: A F
authors.initials: AF
authors.lastname: Cohen
authors.forename: Z
authors.initials: Z
authors.lastname: Diamant
mesh_terms: D000328:Adult; D000485:Allergens / Q000008:administration & dosage; D000818:Animals; D039741:Antigens, Dermatophagoides / Q000008:administration & dosage; D052179:Antigens, Plant / Q000008:administration & dosage; D015415:Biomarkers / Q000378:metabolism; D002415:Cats / Q000276:immunology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009297:Nasal Mucosa / Q000378:metabolism*; D009299:Nasal Provocation Tests; D009569:Nitric Oxide / Q000096:biosynthesis*; D006109:Poaceae / Q000276:immunology; D011058:Pollen / Q000276:immunology; D015203:Reproducibility of Results; D012221:Rhinitis, Allergic, Perennial / Q000175:diagnosis* / Q000378:metabolism; D006255:Rhinitis, Allergic, Seasonal / Q000175:diagnosis* / Q000378:metabolism
chemical_list: D000485:Allergens; D039741:Antigens, Dermatophagoides; D052179:Antigens, Plant; D015415:Biomarkers; D009569:Nitric Oxide