title: C-reactive protein is an independent predictor of severity in community-acquired pneumonia.
abstract: BACKGROUND
  C-reactive protein (CRP) is an acute phase protein synthesized by the liver primarily in response to interleukin-6. Initial studies have suggested that inflammatory markers may have a role in predicting severity. We investigated whether admission and day 4 CRP could predict severity in community-acquired pneumonia.
  
  
  METHODS
  A prospective study was carried out over a 2-year period in a large teaching hospital. CRP was measured on admission and on day 4. The outcomes of interest were: 30-day mortality; need for mechanical ventilation and/or inotropic support; development of complicated pneumonia (lung abscess, empyema, or complicated parapneumonic effusion); the value of predictive tests were assessed using multivariate logistic regression.
  
  
  RESULTS
  There were 570 patients included in the study; 30-day mortality was 9.6%. Low CRP levels showed a high negative predictive value for excluding 30-day mortality (CRP <10 mg/L=100%, CRP <50=99.1%, CRP <100=98.9%, CRP <200=94.9%). Low admission CRP levels <100 mg/L were independently associated with reduced 30-day mortality (odds ratio [OR] 0.18; 0.04-0.85), P=.03; need for mechanical ventilation and/or inotropic support (OR 0.21; 0.14-0.4), P=.002; and complicated pneumonia (OR 0.05; 0.01-0.35), P=.003. A CRP that fails to fall by 50% or more within 4 days of admission is independently associated with increased 30 day mortality (OR 24.5; 6.4-93.4), P <.0001; need for mechanical ventilation and/or inotropic support (OR 7.1; 2.8-17.8), P <.0001 and complicated pneumonia (OR 15.4; 6.32-37.6), P <.0001.
  
  
  CONCLUSIONS
  Admission CRP <100 mg/L has reduced risk for 30-day mortality, need for mechanical ventilation and/or inotropic support, and complicated pneumonia. Failure of CRP to fall by 50% or more at day 4 leads to an increased risk for 30-day mortality, need for mechanical ventilation and/or inotropic support, and complicated pneumonia. C-reactive protein is an independent marker of severity in community-acquired pneumonia.
authors.affiliation: Department of Respiratory Medicine, Royal Infirmary of Edinburgh, Edinburgh, Scotland, UK. jamesdchalmers@googlemail.com
authors.forename: James D
authors.initials: JD
authors.lastname: Chalmers
authors.forename: Aran
authors.initials: A
authors.lastname: Singanayagam
authors.forename: Adam T
authors.initials: AT
authors.lastname: Hill
mesh_terms: D000328:Adult; D000368:Aged; D002097:C-Reactive Protein / Q000378:metabolism*; D002316:Cardiotonic Agents / Q000627:therapeutic use; D017714:Community-Acquired Infections / Q000097:blood* / Q000175:diagnosis* / Q000401:mortality / Q000628:therapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018410:Pneumonia, Bacterial / Q000097:blood* / Q000175:diagnosis* / Q000401:mortality / Q000628:therapy; D011379:Prognosis; D012121:Respiration, Artificial
chemical_list: D002316:Cardiotonic Agents; D002097:C-Reactive Protein