Evaluation of diagnostic performance of Xpert® MTB/RIF Ultra assay in suspected tuberculous meningitis cases in a tertiary care setting

Objectives: Tuberculous meningitis is the most lethal manifestation of tuberculosis. Xpert^® MTB/RIF Ultra is a nucleic acid amplification test which gives result in 80 minutes and simultaneously provides information on rifampicin resistance. This study was carried out to evaluate the diagnostic performance of Xpert Ultra assay.

Materials & Methods: After obtaining ethics permission, cerebrospinal fluid (CSF) of 50 adult cases of clinically suspected tuberculous meningitis were tested by liquid culture, Xpert^® MTB/RIF assay and Xpert^® Ultra assay. 

Statistical analysis: Of the 50 cases, MTB was detected in 16 cases. Of these, three were positive by Xpert^®, 11by Ultra and 12 by culture. Of the six cases that gave trace positive result by ultra, four were negative by Xpert^® and culture. One strain was rifampicin (RIF) resistant by all three methods.

Results: Sensitivity, Specificity, Positive predictive value (PPV) and Negative predictive value (NPV) of Xpert^® Ultra was 58.33%, 89.47% ,63.63% and 87.17% in comparison with liquid culture.

Conclusion: Xpert^® MTB/RIF ultra-assay showed better sensitivity and high negative predictive value when compared to Xpert^® MTB/RIF assay. Hence can be used in suspected cases of TBM to prevent complications like death and serious neurological disability. Trace results do not provide information on rifampicin (RIF) resistance.