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Table 3 Comparison of Xpert MTB/RIF assay test characteristics and diagnostic accuracy when using unconcentrated and concentrated pericardial fluid samples

From: Diagnostic accuracy of quantitative PCR (Xpert MTB/RIF) for tuberculous pericarditis compared to adenosine deaminase and unstimulated interferon-γ in a high burden setting: a prospective study

Pericardial fluid type Indeterminate rate (number/total number of assays performed) Internal positive controlaCT-value (median, IQR) Xpert MTB/RIF positive tests in definite and probable-TB patients
Unconcentrated (1 ml) 2.1% (0.3 to 4.6) 3/138 26.2 (25.1 to 27.4) 41.0% (32.1 to 49.9) 48/117
Concentrated/centrifuged pellet (20 ml) 10.4% (5.3 to 15.6) 14/134 26.2 (25.1 to 27.6) 52.9% (43.9 to 62.0) 62/117
P-valueb 0.005 0.9 0.07
  1. A median of 20 ml of pericardial fluid was centrifuged at 3,000 × g for 15 minutes with the pellet re-suspended in sterile PBS, followed by Xpert MTB. aInternal positive control: to evaluate potential PCR inhibition an unrelated fragment of fungal DNA (Bacillus globigii) is co-amplified in the reaction; b P-values compare unconcentrated and concentrated pericardial fluid samples for particular Xpert. CI, confidence interval; IQR: Interquartile range; TB, tuberculosis,