Limitations of the MTB/RIF Assay: An Xpert Review of 4 Clinical Cases

Allison L Haas; Angela Ma; Jonathan Pham; Punam Verma; Uma Malhotra; E Chandler Church; Masahiro Narita; Vincent Escuyer; Salika M Shakir

doi:10.1093/ofid/ofaf132

Limitations of the MTB/RIF Assay: An Xpert Review of 4 Clinical Cases

Open Forum Infect Dis. 2025 Mar 5;12(4):ofaf132. doi: 10.1093/ofid/ofaf132. eCollection 2025 Apr.

Authors

Allison L Haas^{1

2}, Angela Ma^{1

2}, Jonathan Pham^{1

2}, Punam Verma³, Uma Malhotra^{4

5}, E Chandler Church^{5

6

7}, Masahiro Narita^{7

8}, Vincent Escuyer⁹, Salika M Shakir^{1

2}

Affiliations

¹ Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah, USA.
² Division of Infectious Diseases, ARUP Laboratories, Salt Lake City, Utah, USA.
³ Department of Pathology and Laboratory Medicine, Virginia Mason Medical Center, Seattle, Washington, USA.
⁴ Infectious Diseases, Virginia Mason Franciscan Health, Seattle, Washington, USA.
⁵ Department of Medicine, Division of Allergy and Infectious Diseases, University of Washington, Seattle, Washington, USA.
⁶ Vaccine and Infectious Diseases Division, Fred Hutchinson Cancer Center, Seattle, Washington, USA.
⁷ Seattle & King County Public Health Department, Seattle, Washington, USA.
⁸ Department of Medicine, Division of Pulmonary, Critical Care and Sleep Medicine, University of Washington, Seattle, Washington, USA.
⁹ New York State Department of Health, Wadsworth Center, Albany, New York, USA.

Abstract

Current U.S. Centers for Disease Control and Prevention tuberculosis (TB) guidelines recommend molecular testing for initial diagnosis of TB and detection of rifampin resistance to expedite initiation of proper treatment. The Cepheid Xpert MTB/RIF assay can detect members of the Mycobacterium tuberculosis complex and rifampin resistance by evaluating for mutations in the rpoB gene. However, false-positive and false-negative detection of M tuberculosis and rifampin resistance results can lead to incorrect treatment of patients, including overuse of second-line anti-TB drugs, and may result in patient harm and increased healthcare cost. We present a series of 4 cases to demonstrate the limitations of the Xpert MTB/RIF assay in the diagnosis of TB, emphasizing the importance of follow-up confirmatory testing and laboratory oversight in reporting accurate results.

Keywords: Mycobacterium tuberculosis; Xpert MTB/RIF; rapid diagnostics; rifampin resistance; rpoB mutation.