Diagnostic accuracy of GeneXpert and sputum Zeil Nelson Staining in predicting tuberculosis taking Sputum Culture as Gold standard

Abstract

Background: Tuberculosis (TB) is a highly prevalent infectious disease that can involve any part of the body; the most favored site is lung. Tests used for its diagnosis include sputum Zeil Nelson staining, Gene Xpert, and culture.Objective: Objective of this study was to determine the diagnostic accuracy of GeneXpert and sputum-ZN staining in predicting tuberculosis taking sputum culture as Gold standard.Methodology: This cross sectional validation study was conducted in March 15, 2015 the Pulmonology department, Military Hospital Rawalpindi from September 14, 2015 to 14/09/2015. Patients of both gender aged 18-70 years and pulmonary TB (PTB) suspect were included in the study through consecutive non-probability sampling technique. The sample size was calculated through WHO software, assuming 25% TB prevalence, 95% confidence interval and 10% margin of error. Diagnosed PTB Patients, those on anti-tuberculosis (ATT) treatment, patients with co-morbid like congestive heart failure, Diabetes mellitus, HIV positive and patients on steroids were excluded from the study.Results: Out of 265 patients, 183 (69.1%) were male and 82 (30.9%) female. Mean age was 45.65±14.91 years. Sensitivity and Specificity of Sputum smear microscopy was 68.48% and 74.07% respectively. While PPV, NPV and diagnostic accuracy of sputum smear microscopy was 85.71%, 50.85% and 70.19% respectively. Sensitivity and Specificity of Gene Xpert was 97.83% and 92.59%. However Positive Predictive Value, Negative predictive Value and diagnostic accuracy of Gene Xpert test was 96.77%, 94.94% and 96.23%respectively.Conclusion: GeneXpert is more accurate and reliable than sputummicroscopy in predicting pulmonary TB.