The use of an automated quantitative polymerase chain reaction (Xpert MTB/RIF) to predict the sputum smear status of tuberculosis patients

Xpert MTB/RIF-generated cycle-threshold (C T) values have poor clinical utility as a rule-in test for smear positivity (cut-point ≤20.2; sensitivity 32.3%, specificity 97.1%) but moderately good rule-out value (cut-point >31.8; negative predictive value 80.0%). Thus, 20% of individuals with CT values >31.8 were erroneously ruled out as smear-negative. This group had a significantly lower sputum bacillary load relative to correctly classified smear-positive patients (C T ≤ 31.8; P <. 001). These data inform on public health and contact tracing strategies. © The Author 2011. Published by Oxford University Press on behalf of the Infectious.