Abstract
BackgroundTuberculous pericarditis (TBP) is associated with high morbidity and mortality, and is an important treatable cause of heart failure in developing countries. Tuberculous aetiology of pericarditis is difficult to diagnose promptly. The utility of the new quantitative PCR test (Xpert MTB/RIF) for the diagnosis of TBP is unknown. This study sought to evaluate the diagnostic accuracy of the Xpert MTB/RIF test compared to pericardial adenosine deaminase (ADA) and unstimulated interferon-gamma (uIFNγ) in suspected TBP.MethodsFrom October 2009 through September 2012, 151 consecutive patients with suspected TBP were enrolled at a single centre in Cape Town, South Africa. Mycobacterium tuberculosis culture and/or pericardial histology served as the reference standard for definite TBP. Receiver-operating-characteristic curve analysis was used for selection of ADA and uIFNγ cut-points.ResultsOf the participants, 49% (74/151) were classified as definite TBP, 33% (50/151) as probable TBP and 18% (27/151) as non TBP. A total of 105 (74%) participants were human immunodeficiency virus (HIV) positive. Xpert-MTB/RIF had a sensitivity and specificity (95% confidence interval (CI)) of 63.8% (52.4% to 75.1%) and 100% (85.6% to 100%), respectively. Concentration of pericardial fluid by centrifugation and using standard sample processing did not improve Xpert MTB/RIF accuracy. ADA (≥35 IU/L) and uIFNγ (≥44 pg/ml) both had a sensitivity of 95.7% (88.1% to 98.5%) and a negative likelihood ratio of 0.05 (0.02 to 0.10). However, the specificity and positive likelihood ratio of uIFNγ was higher than ADA (96.3% (81.7% to 99.3%) and 25.8 (3.6 to 183.4) versus 84% (65.4% to 93.6%) and 6.0 (3.7 to 9.8); P = 0.03) at an estimated background prevalence of TB of 30%. The sensitivity and negative predictive value of both uIFNγ and ADA were higher than Xpert-MT/RIF (P < 0.001).ConclusionsuIFNγ offers superior accuracy for the diagnosis of microbiologically confirmed TBP compared to the ADA assay and the Xpert MTB/RIF test.
Highlights
Tuberculous pericarditis (TBP) is associated with high morbidity and mortality, and is an important treatable cause of heart failure in developing countries
pericardial fluid (PF) was sent to the National Health Laboratory Service (NHLS) for measurement of adenosine deaminase (ADA) and lactate dehydrogenase (LDH) levels, differential cell counts and cytology, as well as routine TB diagnosis consisting of concentrated fluorescence smear microscopy and mycobacteria growth indicator tube (MGIT) liquid culture (MGIT 960, BD Diagnostics, Hunt Valley, MD, USA)
The key findings of our study are that: (1) Unstimulated interferon-gamma (uIFNγ) offers superior accuracy for the diagnosis of microbiologically confirmed TBP compared to the new Xpert MTB/RIF test and the established ADA assay; (2) PF Xpert MTB/RIF could bacteriologically confirm a TB diagnosis in two thirds of patients with suspected TBP; (3) PF uIFNγ offered better rule-in diagnostic utility compared to ADA in current clinical use, while both tests could rapidly rule-out TBP; (4) PF Xpert MTB/RIF, when combined with either ADA or uIFNγ, offers >97% sensitivity and specificity for TBP diagnosis; and (5) concentration of PF samples prior to Xpert MTB/ RIF testing increased the number of ‘indeterminate’ tests without significantly improving diagnostic yield
Summary
Tuberculous pericarditis (TBP) is associated with high morbidity and mortality, and is an important treatable cause of heart failure in developing countries. The utility of the new quantitative PCR test (Xpert MTB/RIF) for the diagnosis of TBP is unknown. In developing countries with dual human immunodeficiency virus (HIV) and TB epidemics there continues to be high TB-related mortality [2]. In immunosuppressed patients, this high mortality can be largely attributed to the increased burden of disseminated and severe forms of extra-pulmonary TB, such as tuberculous pericarditis (TBP) [3]. Despite the burden of disease and associated high mortality, the diagnosis of TBP remains problematic because of the lack of a simple, rapid, accessible and accurate diagnostic test [5]. Recent studies have indicated that the rapid initiation of anti-TB treatment may reduce mortality, making the investigation of new, rapid diagnostic tests for TBP essential [8]
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