Correlating Xpert MTB/RIF Results with Sputum Smear Status

In a study involving 130 patients with pulmonary tuberculosis, an Xpert MTB/RIF cycle time >31.8 indicated an 80% likelihood of smear negativity.

The Xpert MTB/RIF is an automated real-time polymerase chain reaction assay that can detect Mycobacterium tuberculosis DNA, as well as the gene encoding for rifampin resistance, in sputum samples. The WHO endorses its use for the frontline diagnosis of tuberculosis (TB). One limitation of this assay is its inability to determine which patients with pulmonary TB have sputum positive for acid-fast bacilli (AFB).

To explore this issue, researchers studied the relation between Xpert MTB/RIF cycle time (C_T; the number of cycles needed for the MTB/RIF assay to detect a genomic signal) and AFB smear status. The study was performed in Cape Town, South Africa, where HIV/TB coinfection is common.

Among 130 patients with positive MTB/RIF assays, 96 were…

Reviewing Author

Neil M. Ampel, MD

Disclosures

Editorial BoardsUpToDate

Leadership Positions in Professional SocietiesCoccidioidomycosis Study Group (Past President, Secretary, Treasurer)

Neil M. Ampel, MD

Disclosures

Editorial BoardsUpToDate

Leadership Positions in Professional SocietiesCoccidioidomycosis Study Group (Past President, Secretary, Treasurer)

Correlating Xpert MTB/RIF Results with Sputum Smear Status

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Reviewing Author