Assessment of diagnostic accuracy of Ziehl-Neelsen microscopy and GeneXpert MTB/ RIF assays from pulmonary and extra pulmonary specimens in a tertiary care hospital setting

Abstract

Objective: To compare the diagnostic accuracy of GeneXpert over ZN microscopy in pulmonary and extra pulmonary suspected tuberculosis samples. Study Design: Retrospective Cross-sectional study. Setting: Tertiary Care Hospital, Rawalpindi. Period: January 2024 to June 2024. Methods: All suspected tuberculosis cases from pulmonary and extra pulmonary samples were subjected to ZN microscopy and Gene Xpert MTB/RIF. Samples irrespective of age and gender were included in the study and spot specimens were excluded. Frequency and percentages were calculated for variables using SPSS v.26. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of ZN microscopy and GeneXpert were also analyzed. Results: Out of total 813 suspected pulmonary tuberculosis (PTB) and extra-pulmonary tuberculosis (EPTB) specimens, 467(57.4%) were males while 346(42.5%) were females. Among all the samples, 695 (85.48%) were pulmonary and 118 (14.51%) were extra-pulmonary samples. The total number of samples stained positive with ZN were 106 (13.03%) whereas, sample detected postive on GeneXpert MTB/RIF were found to be 124 (15.25%). Out of all ZN postive samples detected by ZN staining method, 103 (97%) were PTB and 3 (03%) were EPTB samples. Whereas the positive samples detected by GeneXpert MTB/RIF comprised of 109 (88%) PTB and 15 (12%) were EPTB samples. Furthermore, sensitivity and specificity of Gene Xpert MTB/RIF was found to be 85.48% and 100% respectively, with a 100% PPV and 97.4% NPV in this study. Conclusion: GeneXpert MTB/RIF has a higher sensitivity and specificity compared to conventional ZN smear microscopy. GeneXpert has detected more positive cases from both PTB and EPTB specimens.