Clinical application of a rapid lung-orientated immunoassay in individuals with possible tuberculosis. Issue 1 (3rd August 2007)

• Record Type: Journal Article
• Authors: Breen, R A M; Barry, S M; Smith, C J; Shorten, R J; Dilworth, J P; Cropley, I; McHugh, T D; Gillespie, S H; Janossy, G; Lipman, M C I
• Is Part Of: Thorax. Volume 63:Issue 1(2008)
• Page Start: 67
• Page End: 71
• Publication Date: 2007-08-03
• Subjects: Chest -- Diseases -- Periodicals; Thorax; Chest -- Diseases; Periodicals; Periodicals; 617.54
• DOI: 10.1136/thx.2007.078857
• Languages: English
• ISSNs: 0040-6376

Abstract

Abstract : Background: Immunological ex vivo assays to diagnose tuberculosis (TB) have great potential but have largely been blood-based and poorly evaluated in active TB. Lung sampling enables combined microbiological and immunological testing and uses higher frequency antigen-specific responses than in blood. Methods: A prospective evaluation was undertaken of a flow cytometric assay measuring the percentage of interferon-γ synthetic CD4+ lymphocytes following stimulation with purified protein derivative of Mycobacterium tuberculosis (PPD) in bronchoalveolar lavage fluid from 250 sputum smear-negative individuals with possible TB. A positive assay was defined as >1.5%. Results: Of those who underwent lavage and were diagnosed with active TB, 95% (106/111) had a positive immunoassay (95% CI 89% to 98%). In 139 individuals deemed not to have active TB, 105 (76%) were immunoassay negative (95% CI 68% to 82%). Of the remaining 24% (34 cases) with a positive immunoassay, a substantial proportion had evidence of untreated TB; in two of these active TB was subsequently diagnosed. Assay performance was unaffected by HIV status, disease site or BCG vaccination. In culture-positive pulmonary cases, response to PPD was more sensitive than nucleic acid amplification testing (94% vs 73%). The use of early secretory antigen target-6 (ESAT-6) responses in 71 subjects was no better than PPD, and 19% of those with culture-confirmed TB and a positive PPD immunoassay had no detectable response to ESAT-6. Conclusions: These findings suggest that lung-orientated immunological investigation is a potentially powerful tool in diagnosing individuals with sputum smear-negative active TB, regardless of HIV serostatus.