title: Interferon gamma release assay for differentiating tuberculosis among pneumonia cases in acute healthcare setting.
abstract: OBJECTIVE
  Early diagnosis of smear-negative tuberculosis remains challenging. The role of an interferon-gamma release assay (IGRA) in discriminating active pulmonary tuberculosis (PTB) among cases of 'pneumonia' was investigated.
  
  
  METHODS
  Consecutive patients admitted to an acute hospital in Hong Kong (intermediate TB burden) during 2006-2008 because of pneumonia and suspected PTB were recruited for IGRA (Quantiferon-TB Gold, QFN-G) study. Diagnosis of tuberculosis was confirmed by mycobacterial culture or histology.
  
  
  RESULTS
  Altogether 179 patients were recruited (median (IQR) age 59 (44-75), 68.7% male); active PTB was confirmed in 63 (35.2%). Among the AFB-smear-negative 'pneumonias' (n = 152), age>50 (OR 0.27, 95% CI 0.09-0.84), absence of weight loss (OR 0.30, 95% CI 0.10-0.88), and negative IGRA (OR 0.08, 95% CI 0.03-0.25) were independently associated with lower risks of PTB. The overall sensitivity, specificity, positive and negative predictive values for the IGRA in diagnosing active PTB were 60%, 87%, 72% and 80% respectively. Among smear-negative 'pneumonias' (n = 152), the performance values of IGRA were 64%, 87%, 62% and 88% respectively; in the absence of characteristic clinical or radiographic features of PTB, the negative predictive value (NPV) improved to 90-95%.
  
  
  CONCLUSIONS
  The high NPV of QFN-G among smear-negative 'pneumonias' can be useful for risk stratification in hospitalized patients suspected of PTB. Further investigation on the role of these assays in patient management is warranted.
authors.affiliation: Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong.
authors.forename: G
authors.initials: G
authors.lastname: Lui
authors.forename: N
authors.initials: N
authors.lastname: Lee
authors.forename: S W
authors.initials: SW
authors.lastname: Cheung
authors.forename: J S Y
authors.initials: JS
authors.lastname: Lam
authors.forename: B C K
authors.initials: BC
authors.lastname: Wong
authors.forename: K W
authors.initials: KW
authors.lastname: Choi
authors.forename: K T
authors.initials: KT
authors.lastname: Wong
authors.forename: R Y K
authors.initials: RY
authors.lastname: Wong
authors.forename: C S
authors.initials: CS
authors.lastname: Cockram
authors.forename: D S C
authors.initials: DS
authors.lastname: Hui
authors.forename: R C Y
authors.initials: RC
authors.lastname: Chan
mesh_terms: D000328:Adult; D000368:Aged; D019411:Clinical Laboratory Techniques / Q000379:methods*; D003422:Critical Care / Q000379:methods*; D003937:Diagnosis, Differential; D042241:Early Diagnosis; D005260:Female; D006723:Hong Kong; D006801:Humans; D007118:Immunoassay / Q000379:methods; D007371:Interferon-gamma / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification; D018410:Pneumonia, Bacterial / Q000175:diagnosis*; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis*
chemical_list: D007371:Interferon-gamma