Comparing diagnostic accuracy: Xpert MTB/RIF Ultra vs. Xpert MTB/RIF for diagnosis of pulmonary tuberculosis

With the development of Xpert MTB/RIF (Xpert) and its latest version Xpert MTB/RIF Ultra (Ultra), diagnosis of tuberculosis has improved dramatically. Only few have compared the Ultra to Xpert, especially in varied geographic locations. The ability of Ultra to detect tuberculosis in pulmonary samples was thus compared in the current study to the Xpert for the quick identification of MTBC and resistance to rifampicin (RR) in sputum samples.

Adults and adolescents (>10 years) with suspicion of pulmonary tuberculosis were enrolled for the study. All the samples were subjected to smear microscopy, liquid culture and molecular methods Xpert MTB/RIF as well as Xpert Ultra in parallel.

A total of 143 sputum samples were cultured in liquid media, with 52 of them proved to be culture positive. Using culture as the "reference standard," the Xpert Ultra detected MTBC in 45 samples, with sensitivity and specificity of 86.5% (74.2%-94.4%) and 89.9% (81.0%-95.5%), respectively. While the sensitivity and specificity, of Xpert was found to be 76.9% (63.2%-87.5%) and 93.7% (85.8%-97.9%) respectively. Xpert Ultra also detected 78.8% smear negative culture positive samples in comparison to Xpert MTB/RIF which detected 63.6% smear negative samples.

Xpert Ultra can offer a valid TB diagnosis in a fraction of the time it takes to perform a culture and has higher sensitivity than Xpert MTB/RIF. This is especially true for paucibacillary samples with negative sputum smear.