Fig. 1

Confirming and excluding power of a positive and negative Xpert test, in smear negative PLHIV with presumptive TB. TB: tuberculosis; Xpert: Xpert MTB/RIF; LR: Likelihood ratio; Pos: positive; Neg: negative; CP: confirming power; EP: excluding power. For a given 61% sensitivity and 99% specificity of Xpert MTB/RIF to detect tuberculosis in smear-negative HIV infected patients with presumptive TB [3], the pre-test probability (prevalence) was 17%, the confirming power of a Xpert result showing “TB detected” was 61 (very strong confirming power), and the excluding power of a Xpert result showing “TB not detected” was 3 (weak excluding power) [13]