title: Exhaled carbon monoxide in asthmatics: a meta-analysis.
abstract: BACKGROUND
  The non-invasive assessment of airway inflammation is potentially advantageous in asthma management. Exhaled carbon monoxide (eCO) measurement is cheap and has been proposed to reflect airway inflammation and oxidative stress but current data are conflicting. The purpose of this meta-analysis is to determine whether eCO is elevated in asthmatics, is regulated by steroid treatment and reflects disease severity and control.
  
  
  METHODS
  A systematic search for English language articles published between 1997 and 2009 was performed using Medline, Embase and Cochrane databases. Observational studies comparing eCO in non-smoking asthmatics and healthy subjects or asthmatics before and after steroid treatment were included. Data were independently extracted by two investigators and analyzed to generate weighted mean differences using either a fixed or random effects meta-analysis depending upon the degree of heterogeneity.
  
  
  RESULTS
  18 studies were included in the meta-analysis. The eCO level was significantly higher in asthmatics as compared to healthy subjects and in intermittent asthma as compared to persistent asthma. However, eCO could not distinguish between steroid-treated asthmatics and steroid-free patients nor separate controlled and partly-controlled asthma from uncontrolled asthma in cross-sectional studies. In contrast, eCO was significantly reduced following a course of corticosteroid treatment.
  
  
  CONCLUSIONS
  eCO is elevated in asthmatics but levels only partially reflect disease severity and control. eCO might be a potentially useful non-invasive biomarker of airway inflammation and oxidative stress in nonsmoking asthmatics.
authors.affiliation: Department of Respiratory Disease, The First Affiliated Hospital of Nanjing Medical University, Nanjing, China.
authors.forename: Jingying
authors.initials: J
authors.lastname: Zhang
authors.forename: Xin
authors.initials: X
authors.lastname: Yao
authors.forename: Rongbin
authors.initials: R
authors.lastname: Yu
authors.forename: Jianling
authors.initials: J
authors.lastname: Bai
authors.forename: Yun
authors.initials: Y
authors.lastname: Sun
authors.forename: Mao
authors.initials: M
authors.lastname: Huang
authors.forename: Ian M
authors.initials: IM
authors.lastname: Adcock
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Barnes
mesh_terms: D000328:Adult; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D015415:Biomarkers / Q000378:metabolism; D001944:Breath Tests; D002248:Carbon Monoxide / Q000378:metabolism*; D002648:Child; D045853:Exhalation; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism*; D018384:Oxidative Stress; D011237:Predictive Value of Tests; D012720:Severity of Illness Index; D013256:Steroids / Q000627:therapeutic use; D016896:Treatment Outcome; D015854:Up-Regulation
chemical_list: D018927:Anti-Asthmatic Agents; D015415:Biomarkers; D018836:Inflammation Mediators; D013256:Steroids; D002248:Carbon Monoxide