title: Rapid diagnosis of smear-negative tuberculosis using immunology and microbiology with induced sputum in HIV-infected and uninfected individuals.
abstract: OBJECTIVE
  Blood-based studies have demonstrated the potential of immunological assays to detect tuberculosis. However lung fluid sampling may prove superior as it enables simultaneous microbiological detection of mycobacteria to be performed. Until now this has only been possible using the expensive and invasive technique of broncho-alveolar lavage. We sought to evaluate an immunoassay using non-invasive induced-sputum to diagnose active tuberculosis.
  
  
  RESULTS
  Prospective cohort study of forty-two spontaneous sputum smear-negative or sputum non-producing adults under investigation for tuberculosis. CD4 lymphocytes specific to purified-protein-derivative of Mycobacterium tuberculosis actively synthesising interferon-gamma were measured by flow cytometry and final diagnosis compared to immunoassay using a cut-off of 0.5%. Sixteen subjects (38%) were HIV-infected (median CD4 count [range] = 332 cells/microl [103-748]). Thirty-eight (90%) were BCG-vaccinated. In 27 subjects diagnosed with active tuberculosis, the median [range] percentage of interferon-gamma synthetic CD4+ lymphocytes was 2.77% [0-23.93%] versus 0% [0-2.10%] in 15 negative for active infection (p<0.0001). Sensitivity and specificity of the immunoassay versus final diagnosis of active tuberculosis were 89% (24 of 27) and 80% (12 of 15) respectively. The 3 positive assays in the latter group occurred in subjects diagnosed with quiescent/latent tuberculosis. Assay performance was unaffected by HIV-status, BCG-vaccination or disease site. Combining this approach with traditional microbiological methods increased the diagnostic yield to 93% (25 of 27) alongside acid-fast bacilli smear and 96% (26 of 27) alongside tuberculosis culture.
  
  
  CONCLUSIONS
  These data demonstrate for the first time that a rapid immunological assay to diagnose active tuberculosis can be performed successfully in combination with microbiological methods on a single induced-sputum sample.
authors: Department of Immunology, Royal Free & University College Medical School, London, United Kingdom. ronan.breen@gstt.nhs.uk
authors: Ronan A M
authors: RA
authors: Breen
authors: Gareth A D
authors: GA
authors: Hardy
authors: Felicity M R
authors: FM
authors: Perrin
authors: Sara
authors: S
authors: Lear
authors: Sabine
authors: S
authors: Kinloch
authors: Colette J
authors: CJ
authors: Smith
authors: Ian
authors: I
authors: Cropley
authors: George
authors: G
authors: Janossy
authors: Marc C I
authors: MC
authors: Lipman
mesh_terms: D000328:Adult; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D015658:HIV Infections / Q000150:complications*; D018023:HIV Seronegativity; D006801:Humans; D008875:Middle Aged; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D014376:Tuberculosis / Q000150:complications / Q000175:diagnosis* / Q000276:immunology / Q000382:microbiology