The Bottom Line: The Xpert MTB/RIF assay has a sensitivity that is roughly two orders of magnitude greater than that of smear microscopy.
Reference: Lawn SD, Mwaba P, Bates M, Piatek A, Alexander H, Marais BJ, Cuevas LE, McHugh TD, Zijenah L, Kapata N, Abubakar I, McNerney R, Hoelscher M,Memish ZA, Migliori GB, Kim P, Maeurer M, Schito M, Zumla A. Advances in tuberculosis diagnostics: the Xpert MTB/RIF assay and future prospects for a point-of-care test. Lancet Infect Dis. 2013 Apr;13(4):349-61.
Summary: Using culture as the reference standard, four of these studies reported that the sensitivity of the Xpert MTB/RIF assay for pulmonary tuberculosis was about two to three times higher than that of smear microscopy when testing induced sputum, nasopharyngeal aspirates, and gastric aspirate lavages. See Table 1, p. 352.