title: Patterns of c-reactive protein RATIO response in severe community-acquired pneumonia: a cohort study.
abstract: BACKGROUND
  Community-acquired pneumonia (CAP) requiring intensive care unit (ICU) admission remains a severe medical condition, presenting ICU mortality rates reaching 30%. The aim of this study was to assess the value of different patterns of C-reactive protein (CRP)-ratio response to antibiotic therapy in patients with severe CAP requiring ICU admission as an early maker of outcome.
  
  
  METHODS
  In total, 191 patients with severe CAP were prospectively included and CRP was sampled every other day from D1 to D7 of antibiotic prescription. CRP-ratio was calculated in relation to D1 CRP concentration. Patients were classified according to an individual pattern of CRP-ratio response with the following criteria: fast response - when D5 CRP was less than or equal to 0.4 of D1 CRP concentration; slow response - when D5 CRP was > 0.4 and D7 less than or equal to 0.8 of D1 CRP concentration; nonresponse - when D7 CRP was > 0.8 of D1 CRP concentration. Comparison between ICU survivors and non-survivors was performed.
  
  
  RESULTS
  CRP-ratio from D1 to D7 decreased faster in survivors than in non-survivors (p = 0.01). The ability of CRP-ratio by D5 to predict ICU outcome assessed by the area under the ROC curve was 0.73 (95% Confidence Interval, 0.64 - 0.82). By D5, a CRP concentration above 0.5 of the initial level was a marker of poor outcome (sensitivity 0.81, specificity 0.58, positive likelihood ratio 1.93, negative likelihood ratio 0.33). The time-dependent analysis of CRP-ratio of the three patterns (fast response n = 66; slow response n = 81; nonresponse n = 44) was significantly different between groups (p < 0.001). The ICU mortality rate was considerably different according to the patterns of CRP-ratio response: fast response 4.8%, slow response 17.3% and nonresponse 36.4% (p < 0.001).
  
  
  CONCLUSIONS
  In severe CAP, sequential evaluation of CRP-ratio was useful in the early identification of patients with poor outcome. The evaluation of CRP-ratio pattern of response to antibiotics during the first week of therapy was useful in the recognition of the individual clinical evolution.
authors.affiliation: Polyvalent Intensive Care Unit, Hospital de São Francisco Xavier, Centro Hospitalar de Lisboa Ocidental, Lisbon, Portugal. luismiguelcoelho16@gmail.com
authors.forename: Luís M
authors.initials: LM
authors.lastname: Coelho
authors.forename: Jorge I F
authors.initials: JI
authors.lastname: Salluh
authors.forename: Márcio
authors.initials: M
authors.lastname: Soares
authors.forename: Fernando A
authors.initials: FA
authors.lastname: Bozza
authors.forename: Juan Carlos R
authors.initials: JC
authors.lastname: Verdeal
authors.forename: Hugo C
authors.initials: HC
authors.lastname: Castro-Faria-Neto
authors.forename: José Roberto
authors.initials: JR
authors.lastname: Lapa e Silva
authors.forename: Patrícia T
authors.initials: PT
authors.lastname: Bozza
authors.forename: Pedro
authors.initials: P
authors.lastname: Póvoa
mesh_terms: D018806:APACHE; D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D015415:Biomarkers / Q000378:metabolism; D002097:C-Reactive Protein / Q000378:metabolism*; D016009:Chi-Square Distribution; D015331:Cohort Studies; D017714:Community-Acquired Infections / Q000188:drug therapy* / Q000382:microbiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000188:drug therapy* / Q000382:microbiology; D011446:Prospective Studies; D012372:ROC Curve; D018709:Statistics, Nonparametric; D015996:Survival Rate; D016896:Treatment Outcome
chemical_list: D000900:Anti-Bacterial Agents; D015415:Biomarkers; D002097:C-Reactive Protein