title: Infection biomarkers in primary care patients with acute respiratory tract infections-comparison of Procalcitonin and C-reactive protein.
abstract: BACKGROUND
  There is a lack of studies comparing the utility of C-reactive protein (CRP) with Procalcitonin (PCT) for the management of patients with acute respiratory tract infections (ARI) in primary care. Our aim was to study the correlation between these markers and to compare their predictive accuracy in regard to clinical outcome prediction.
  
  
  METHODS
  This is a secondary analysis using clinical and biomarker data of 458 primary care patients with pneumonic and non-pneumonic ARI. We used correlation statistics (spearman's rank test) and multivariable regression models to assess association of markers with adverse outcome, namely days with restricted activities and persistence of discomfort from infection at day 14.
  
  
  RESULTS
  At baseline, CRP and PCT did not correlate well in the overall population (r(2) = 0.16) and particularly in the subgroup of patients with non-pneumonic ARI (r(2) = 0.08). Low correlation of biomarkers were also found when comparing cut-off ranges, day seven levels or changes from baseline to day seven. High baseline levels of CRP (>100 mg/dL, regression coefficient 1.6, 95 % CI 0.5 to 2.6, sociodemographic-adjusted model) as well as PCT (>0.5ug/L regression coefficient 2.0, 95 % CI 0.0 to 4.0, sociodemographic-adjusted model) were significantly associated with larger number of days with restricted activities. There were no associations of either biomarker with persistence of discomfort at day 14.
  
  
  CONCLUSIONS
  CRP and PCT levels do not well correlate, but both have moderate prognostic accuracy in primary care patients with ARI to predict clinical outcomes. The low correlation between the two biomarkers calls for interventional research comparing these markers head to head in regard to their ability to guide antibiotic decisions.
  
  
  BACKGROUND
  Current Controlled Trials, ISRCTN73182671.
authors.affiliation: University Department of Medicine, Kantonsspital Aarau, Tellstrasse 5001, Aarau, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Meili
authors.affiliation: University Department of Medicine, Kantonsspital Aarau, Tellstrasse 5001, Aarau, Switzerland.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kutz
authors.affiliation: Basel Institute for Clinical Epidemiology and Biostatistics, Department of Clinical Research, University Hospital Basel, Basel, Switzerland.|Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Canada.
authors.forename: Matthias
authors.initials: M
authors.lastname: Briel
authors.affiliation: Division of Endocrinology, Diabetology and Clinical Nutrition, University Hospital Basel, Basel, Switzerland.
authors.forename: Mirjam
authors.initials: M
authors.lastname: Christ-Crain
authors.affiliation: Basel Institute for Clinical Epidemiology and Biostatistics, Department of Clinical Research, University Hospital Basel, Basel, Switzerland.
authors.forename: Heiner C
authors.initials: HC
authors.lastname: Bucher
authors.affiliation: University Department of Medicine, Kantonsspital Aarau, Tellstrasse 5001, Aarau, Switzerland.
authors.forename: Beat
authors.initials: B
authors.lastname: Mueller
authors.affiliation: University Department of Medicine, Kantonsspital Aarau, Tellstrasse 5001, Aarau, Switzerland. schuetzph@gmail.com.
authors.forename: Philipp
authors.initials: P
authors.lastname: Schuetz
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D015415:Biomarkers / Q000378:metabolism; D001991:Bronchitis / Q000188:drug therapy / Q000378:metabolism; D002097:C-Reactive Protein / Q000378:metabolism*; D002116:Calcitonin / Q000378:metabolism*; D015740:Calcitonin Gene-Related Peptide; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010033:Otitis Media / Q000188:drug therapy / Q000378:metabolism; D010612:Pharyngitis / Q000188:drug therapy / Q000378:metabolism; D011014:Pneumonia / Q000188:drug therapy / Q000378:metabolism*; D011320:Primary Health Care; D011379:Prognosis; D011498:Protein Precursors / Q000378:metabolism*; D012141:Respiratory Tract Infections / Q000188:drug therapy / Q000378:metabolism; D012220:Rhinitis / Q000188:drug therapy / Q000378:metabolism; D012852:Sinusitis / Q000188:drug therapy / Q000378:metabolism; D014069:Tonsillitis / Q000188:drug therapy / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D015415:Biomarkers; C000606589:CALCA protein, human; D011498:Protein Precursors; D002116:Calcitonin; D002097:C-Reactive Protein; D015740:Calcitonin Gene-Related Peptide
keywords: Acute respiratory tract infection; C-reactive protein; Outcome; Primary care; Procalcitonin