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Xpert MTB/RIF test for tuberculosis

2011; Elsevier BV; Volume: 378; Issue: 9790 Linguagem: Inglês

10.1016/s0140-6736(11)61242-7

1474-547X

Grant Theron, Jonny Peter, Keertan Dheda,

Diagnosis and treatment of tuberculosis

We would like to congratulate Catharina Boehme and colleagues (April 30, p 1495)1Boehme CC Nicol MP Nabeta P et al.Feasibility, diagnostic accuracy, and effectiveness of decentralised use of the Xpert MTB/RIF test for diagnosis of tuberculosis and multidrug resistance: a multicentre implementation study.Lancet. 2011; 377: 1495-1505Summary Full Text Full Text PDF PubMed Scopus (772) Google Scholar on their study, the results of which show the excellent performance of Xpert MTB/RIF in health facilities in high-burden, resource-poor settings. The sensitivity of Xpert MTB/RIF was not reduced in individuals infected with HIV compared with those who were uninfected and convincingly outperformed smear microscopy. Thus, Xpert MTB/RIF represents a fundamental advance in the diagnosis of tuberculosis. We have shown a diminished negative predictive value (NPV) and negative likelihood ratio (LR) of Xpert MTB/RIF for the detection of tuberculosis in individuals infected with HIV versus those who were uninfected,2Theron G Peter J van Zyl-Smit R et al.Evaluation of the Xpert MTB/RIF assay for the diagnosis of pulmonary tuberculosis in a high HIV prevalence setting.Am J Respir Crit Care Med. 2011; 184: 132-140Crossref PubMed Scopus (242) Google Scholar suggesting that substantial numbers of patients infected with HIV who are negative by Xpert MTB/RIF actually have active tuberculosis. The likelihood of this false-negativity occurring increased with advanced immunosuppression. The conclusiveness of our findings was limited by our retrospective study design and small sample size. However, these data have now been prospectively confirmed in 6648 patients by Boehme and colleagues. In their study, the NPV was 91·3% (389/426; 95% CI 88·3–93·6) in patients infected with HIV versus 96·0% (748/779; 94·4–97·2; p<0·001) in those who were uninfected; the respective negative LRs were 0·18 (0·17–0·19) versus 0·09 (0·09–0·10). Thus, about one in ten people who are infected with HIV and have active tuberculosis will have a negative test result. These findings were not commented on by Boehme and colleagues. Xpert MTB/RIF has been specifically recommended by WHO as a frontline diagnostic test in individuals suspected of having tuberculosis and HIV co-infection.3Stop TB DepartmentWHORoadmap for rolling out Xpert MTB/RIF for rapid diagnosis of TB and MDR-TB.http://www.who.int/tb/laboratory/roadmap_xpert_mtb-rif.pdfGoogle Scholar, 4Strategic and Technical Advisory Group for Tuberculosis (STAG-TB)Report of the tenth meeting.http://www.who.int/tb/advisory_bodies/stag_tb_report_2010.pdfGoogle Scholar Although Xpert MTB/RIF comprehensively outperforms smear microscopy, and is thus a substantial advance over the standard of care in people with HIV infection, these data highlight the need to treat a single negative result in people with HIV infection with caution. To advance the laudable work by Boehme and colleagues, studies are now required to clarify how people with HIV infection and negative Xpert MTB/RIF results are further investigated and managed given that Xpert MTB/RIF is likely to be used where culture is not available. We declare that we have no conflicts of interest. Xpert MTB/RIF test for tuberculosis – Authors' replyIn response to our paper on Xpert MTB/RIF,1 Grant Theron and colleagues point out that a proportion of patients with tuberculosis, importantly some infected with HIV, will not be detected by Xpert testing. Clearly patients who expectorate very low concentrations of organisms could be misdiagnosed with all existing methods. In the case of microscopy and HIV-associated tuberculosis, this dilemma is acute. Xpert testing greatly diminishes, but does not eliminate, the likelihood that some tuberculosis will be missed. Full-Text PDF