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

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.