Comparative Analysis of Genexpert MTB/Rif version 4 and Genexpert MTB/Rif Ultra on Frozen Sputum

Abstract

Objectives: The aim of this study was to carry out a comparative analysis using Genexpert MTB/Rif Ultra (Ultra) on clinical samples of frozen sputum previously analyzed on Genexpert MTB/Rif version 4 (Xpert)and Mycobacterium Growth Indicator Tube (MGIT) culture.
Design: The study employed both retrospective and prospective cross sectional design.
Setting: Mutare Provincial Hospital Manicaland, Zimbabwe.
Subjects: One hundred and nine de-identified frozen sputum.
Interventions: Ultra test.
Main Outcome Measures: Ultra results.
Results: There was 96/109 (88%) concordance and 10/109 (9.2%) discordance between Xpert and Ultra. Sputum frozen for 7 years then analyzed on Ultra performed better than 7 years previously when it was analyzed as raw sputum on Xpert using MGIT as gold standard (95.6% and 93.2% respectively).The results were comparable and statistically significant, kappa analysis between Xpert and frozen sputum Ultra was not statistically significant showing a slight level of agreement of 0.147 (p value =0.079), 95% CI (-0.1078, 0.4018).
Conclusion: Results of Ultra on frozen sputum correlate reasonably well. The study findings show that TB positive frozen sputum from presumptive DRTB, run on Ultra after 7 years freezing can perform better than previously run Xpert results compared to MGIT as gold standard. In light of the research findings, potential implication are that to save on cost, comparison of performance of newly diagnosed tests can be done using frozen sputum, pre run on panel of TB tests.