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Utility of quantitative T-cell responses versus unstimulated interferon- for the diagnosis of pleural tuberculosis

¹ Lung Infection and Immunity Unit and Centre for Tuberculosis Research and Innovation, University of Cape Town Lung Institute and Division of Pulmonology, Dept of Medicine, University of Cape Town, ² Institute of Infectious Disease and Molecular Medicine, University of Cape Town ⁵ National Health Laboratory Service, Division of Anatomical Pathology, and ⁶ National Health Laboratory Service, Division of Medical Microbiology, Dept of Clinical Laboratory Sciences, University of Cape Town, Cape Town, South Africa. ³ Centre for Infectious Disease and International Health, Dept of Infection, University College Medical School, London, UK. ⁴ Dept of Biomedical Sciences, University of Sassari, Sassari, Italy.

CORRESPONDENCE: K. Dheda, Lung Infection and Immunity Unit, Division of Pulmonology, Dept of Medicine, University of Cape Town, J flr, Old Main Bldg, Groote Schuur Hospital, Observatory, Cape Town, 7925, South Africa. E-mail: keertan.dheda{at}uct.ac.za

Keywords: Diagnosis, diagnostic accuracy, human, interferon-, pleural effusion, tuberculosis

Received: January 13, 2009
Accepted April 7, 2009

The clinical utility of antigen-specific interferon (IFN)- release assays (IGRAs) using pleural mononuclear cells, for the diagnosis of tuberculosis (TB), requires clarification.

We compared the diagnostic utility of unstimulated pleural IFN- levels with several pleural antigen-specific T-cell IGRAs (early secretory antigenic target-6 and culture filtrate protein-10 (T-SPOT.®TB, QuantiFERON®-TB Gold In-tube), purified protein derivative (PPD) and heparin-binding haemagglutinin (HBHA)) in 78 South African TB suspects. Test results were compared against a clinical score and a reference standard.

Out of 74 evaluable subjects 48, seven and 19 had definite, probable and no TB, respectively. 11 (15%) out of 74 pleural samples (nine (19%) out of 48 of the definite TB cases) had total cell counts that were inadequate for T-cell processing. In the remaining 63 samples, the sensitivity, specificity, positive predictive value and negative predictive value of different diagnostic methods were as follows. Maximal bioclinical score: 54, 89, 92 and 43%, respectively; T-SPOT.®TB: 86, 60, 84 and 64%, respectively; QuantiFERON®-TB Gold In-tube: 57, 80, 87 and 44%, respectively; HBHA-specific IGRA: 59, 31, 64 and 27%, respectively; PPD-specific IGRA: 81, 40, 76 and 46%, respectively; and pleural fluid unstimulated IFN-: 97, 100, 100 and 94%, respectively.

Unstimulated IFN- was the most accurate test for distinguishing TB from non-TB effusions in a high-burden setting. The antigen-specific T-cell IGRAs were limited by suboptimal accuracy and the inability to isolate sufficient mononuclear cells to perform the assay.