title: Risk prediction with procalcitonin and clinical rules in community-acquired pneumonia.
abstract: OBJECTIVE
  The Pneumonia Severity Index and CURB-65 predict outcomes in community-acquired pneumonia but have limitations. Procalcitonin, a biomarker of bacterial infection, may provide prognostic information in community-acquired pneumonia. Our objective is to describe the pattern of procalcitonin in community-acquired pneumonia and determine whether procalcitonin provides prognostic information beyond the Pneumonia Severity Index and CURB-65.
  
  
  METHODS
  We conducted a multicenter prospective cohort study in 28 community and teaching emergency departments. Patients presenting with a clinical and radiographic diagnosis of community-acquired pneumonia were enrolled. We stratified procalcitonin levels a priori into 4 tiers: I: less than 0.1; II: greater than 0.1 to less than 0.25; III: greater than 0.25 to less than 0.5; and IV: greater than 0.5 ng/mL. Primary outcome was 30-day mortality.
  
  
  RESULTS
  One thousand six hundred fifty-one patients formed the study cohort. Procalcitonin levels were broadly spread across tiers: 32.8% (I), 21.6% (II), 10.2% (III), and 35.4% (IV). Used alone, procalcitonin had modest test characteristics: specificity (35%), sensitivity (92%), positive likelihood ratio (1.41), and negative likelihood ratio (0.22). Adding procalcitonin to the Pneumonia Severity Index in all subjects minimally improved performance. Adding procalcitonin to low-risk Pneumonia Severity Index subjects (classes I to III) provided no additional information. However, subjects in procalcitonin tier I had low 30-day mortality, regardless of clinical risk, including those in higher risk classes (1.5% versus 1.6% for those in Pneumonia Severity Index classes I to III versus classes IV/V). Among high-risk Pneumonia Severity Index subjects (classes IV/V), one quarter (126/546) were in procalcitonin tier I, and the negative likelihood ratio of procalcitonin tier I was 0.09. Procalcitonin tier I was also associated with lower burden of other adverse outcomes. Similar results were observed with CURB-65 stratification.
  
  
  CONCLUSIONS
  Selective use of procalcitonin as an adjunct to existing rules may offer additional prognostic information in high-risk patients.
authors.affiliation: Clinical Research, Investigation, and Systems Modeling of Acute Illness Laboratory, Department of Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Huang
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Weissfeld
authors.forename: John A
authors.initials: JA
authors.lastname: Kellum
authors.forename: Donald M
authors.initials: DM
authors.lastname: Yealy
authors.forename: Lan
authors.initials: L
authors.lastname: Kong
authors.forename: Michael
authors.initials: M
authors.lastname: Martino
authors.forename: Derek C
authors.initials: DC
authors.lastname: Angus
mesh_terms: D000368:Aged; D015415:Biomarkers / Q000097:blood; D002116:Calcitonin / Q000097:blood*; D015740:Calcitonin Gene-Related Peptide; D017714:Community-Acquired Infections / Q000097:blood* / Q000401:mortality; D005260:Female; D006801:Humans; D016013:Likelihood Functions; D008297:Male; D011014:Pneumonia / Q000097:blood* / Q000401:mortality; D011379:Prognosis; D011446:Prospective Studies; D011498:Protein Precursors / Q000097:blood*; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D016019:Survival Analysis
chemical_list: D015415:Biomarkers; C000606589:CALCA protein, human; D011498:Protein Precursors; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide