Cepheid Xpert MTB Update
Cepheid Xpert MTB is a rapid qualitative PCR that was licensed by the Food and Drug Administration (FDA) in 2014 for direct testing of sputum samples for Mycobacterium tuberculosis (MTB) and simultaneous detection of the rifampin-resistance rpoB gene.
CDC published updated performance characteristics for Cepheid Xpert MTB (Mycobacterium tuberculosis) PCR in 2015 (MMWR 64(07);193). Based on results of a multicenter international study, results from one or two sputum specimens are as reliable as results obtained when multiple specimens are submitted.
A single Xpert MTB PCR test detected 97% of AFB smear-positive, culture-positive MTB patients, while two serial Xpert MTB PCR tests detected 100%. The negative predictive value of a single negative Xpert MTB PCR result was 99.6% calculated for United States MTB disease prevalence. Finally, a single Xpert MTB PCR assay detected 55% of AFB smear-negative, culture-positive specimens, while two successive tests improved recovery to 69%.
Consequently, the FDA has cleared the Xpert MTB/RIF Assay with an expanded intended use that includes testing of either one or two sputum specimens as an alternative to examination of serial acid-fast stained sputum smears to aid in the decision of whether continued airborne infection isolation is warranted for patients with suspected pulmonary tuberculosis.
