Table 5– False positive, false negative and predictive values for rifampicin resistance using Xpert MTB/RIF#
Rifampicin resistance prevalence %PPV %NPV %True positiveFalse negativeFalse positiveTrue negative
132.499.99.50.519.8970.2
249.299.919119.6960.4
359.599.828.51.519.4950.6
466.499.838219.2940.8
571.499.747.52.519931
675.299.757318.8921.2
778.199.666.53.518.6911.4
880.599.676418.4901.6
982.499.585.54.518.2891.8
1084.199.495518882
1185.499.4104.55.517.8872.2
1286.699.3114617.6862.4
1387.799.2123.56.517.4852.6
1488.599.2133717.2842.8
1589.399.1142.57.517833
2092.298.71901016784
2594.198.3237.512.515735
  • PPV: positive predictive value; NPV: negative predictive value. #: according to varying prevalences of rifampicin resistance in a sample population of 1000 individuals; : sensitivity (95%) and specificity (98%) for Xpert MTB/RIF rifampicin resistance, compared with reference method (culture).