title: Diagnostic accuracy of C-reactive protein and procalcitonin in suspected community-acquired pneumonia adults visiting emergency department and having a systematic thoracic CT scan.
abstract: BACKGROUND
  Community-acquired pneumonia (CAP) requires prompt treatment, but its diagnosis is complex. Improvement of bacterial CAP diagnosis by biomarkers has been evaluated using chest X-ray infiltrate as the CAP gold standard, producing conflicting results. We analyzed the diagnostic accuracy of biomarkers in suspected CAP adults visiting emergency departments for whom CAP diagnosis was established by an adjudication committee which founded its judgment on a systematic multidetector thoracic CT scan.
  
  
  METHODS
  In an ancillary study of a multi-center prospective study evaluating the impact of systematic thoracic CT scan on CAP diagnosis, sensitivity and specificity of C-reactive protein (CRP) and procalcitonin (PCT) were evaluated. Systematic nasopharyngeal multiplex respiratory virus PCR was performed at inclusion. An adjudication committee classified CAP diagnostic probability on a 4-level Likert scale, based on all available data.
  
  
  RESULTS
  Two hundred patients with suspected CAP were analyzed. The adjudication committee classified 98 patients (49.0 %) as definite CAP, 8 (4.0 %) as probable, 23 (11.5 %) as possible and excluded in 71 (35.5 %, including 29 patients with pulmonary infiltrates on chest X-ray). Among patients with radiological pulmonary infiltrate, 23 % were finally classified as excluded. Viruses were identified by PCR in 29 % of patients classified as definite. Area under the curve was 0.787 [95 % confidence interval (95 % CI), 0.717 to 0.857] for CRP and 0.655 (95 % CI, 0.570 to 0.739) for PCT to detect definite CAP. CRP threshold at 50 mg/L resulted in a positive predictive value of 0.76 and a negative predictive value of 0.75. No PCT cut-off resulted in satisfactory positive or negative predictive values. CRP and PCT accuracy was not improved by exclusion of the 25 (25.5 %) definite viral CAP cases.
  
  
  CONCLUSIONS
  For patients with suspected CAP visiting emergency departments, diagnostic accuracy of CRP and PCT are insufficient to confirm the CAP diagnosis established using a gold standard that includes thoracic CT scan. Diagnostic accuracy of these biomarkers is also insufficient to distinguish bacterial CAP from viral CAP.
  
  
  BACKGROUND
  ClinicalTrials.gov registry NCT01574066 (February 7, 2012).
authors.affiliation: Department of General Practice, University Paris Diderot, Sorbonne Paris Cité, 16 rue Henri Huchard, 75018, Paris, France. josselin.lebel@univ-paris-diderot.fr.|UMR 1137, INSERM, IAME, Paris, France. josselin.lebel@univ-paris-diderot.fr.
authors.forename: Josselin
authors.initials: J
authors.lastname: Le Bel
authors.affiliation: University Pierre et Marie Curie, Paris, France. pierre.hausfater@aphp.fr.|Emergency Department, University Hospital Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris (AP-HP), Paris, France. pierre.hausfater@aphp.fr.
authors.forename: Pierre
authors.initials: P
authors.lastname: Hausfater
authors.affiliation: Department of Automated Biological Diagnosis, University Hospitals Cochin-Broca-Hôtel Dieu, HUPC, Assistance Publique-Hôpitaux de Paris (AP-HP), 75014, Paris, France. camille.gobeaux@aphp.fr.
authors.forename: Camille
authors.initials: C
authors.lastname: Chenevier-Gobeaux
authors.affiliation: University of Nantes, Nantes, France. xavier.blanc@chu-nantes.fr.|University Hospital Nantes, Institut du Thorax, Service de Pneumologie, Nantes, France. xavier.blanc@chu-nantes.fr.
authors.forename: François-Xavier
authors.initials: FX
authors.lastname: Blanc
authors.affiliation: Department of Radiology, University Hospital Tenon, 75020, Paris, France. mikhael.benjoar@gmail.com.
authors.forename: Mikhael
authors.initials: M
authors.lastname: Benjoar
authors.affiliation: Infectious Disease Department, Bégin Military Teaching Hospital, 94163, Saint-Mandé cedex, France. cecile.ficko@yahoo.fr.
authors.forename: Cécile
authors.initials: C
authors.lastname: Ficko
authors.affiliation: Emergency Department, University Hospital Tenon, Assistance Publique-Hôpitaux de Paris (AP-HP), University Pierre et Marie Curie, 75020, Paris, France. patrick.ray@aphp.fr.
authors.forename: Patrick
authors.initials: P
authors.lastname: Ray
authors.affiliation: Emergency Department, University Hospital Bichat-Claude Bernard, Assistance Publique-Hôpitaux de Paris (AP-HP), 75018, Paris, France. christophe.choquet@aphp.fr.
authors.forename: Christophe
authors.initials: C
authors.lastname: Choquet
authors.affiliation: UMR 1137, INSERM, IAME, Paris, France. xavier.duval@aphp.fr.|Inserm CIC 1425, University Hospital Bichat-Claude Bernard, Assistance Publique-Hôpitaux de Paris (AP-HP), 75018, Paris, France. xavier.duval@aphp.fr.|University Paris Diderot, Sorbonne Paris Cité, 75018, Paris, France. xavier.duval@aphp.fr.
authors.forename: Xavier
authors.initials: X
authors.lastname: Duval
authors.affiliation: Emergency Department, Hospital Princesse Grace, Monaco, Monaco. yann-erick.claessens@chpg.mc.
authors.forename: Yann-Erick
authors.initials: YE
authors.lastname: Claessens
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood*; D002097:C-Reactive Protein / Q000032:analysis / Q000378:metabolism*; D002116:Calcitonin / Q000032:analysis / Q000378:metabolism*; D015740:Calcitonin Gene-Related Peptide; D017714:Community-Acquired Infections / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000175:diagnosis* / Q000473:pathology; D011446:Prospective Studies; D011498:Protein Precursors / Q000032:analysis / Q000378:metabolism*; D013902:Radiography, Thoracic / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D015415:Biomarkers; C000606589:CALCA protein, human; D011498:Protein Precursors; D002116:Calcitonin; D002097:C-Reactive Protein; D015740:Calcitonin Gene-Related Peptide