Role of Genexpert in Extra Pulmonary Tuberculosis

Overview

Diagnosis of extra pulmonary tuberculosis remains especially challenging since the number of Mycobacterium tuberculosis bacilli present in tissues at sites of disease is often low and clinical specimens from deep-seated organs may be difficult to obtain. Histology is time-consuming to undertake and establishing a diagnosis of tuberculosis with high specificity remains difficult. Tissue microscopy after special staining is often negative and when mycobacteria are seen, it is impossible to distinguish Mycobacterium tuberculosis from non tuberculous mycobacterial disease. Reliance on culture, the mainstay of diagnosis, often leads to considerable delays, compromising patient care and outcomes. Evidence from 138 studies published before 2008 suggested that nucleic acid amplification technologies could not replace conventional mycobacterial tests (microscopy, culture) for diagnosing pulmonary and, especially, extra pulmonary tuberculosis

Only a few years later, GeneXpert technology has changed this paradigm, with a recent systematic review showing pooled sensitivity of 88% and pooled specificity of 98% for diagnosis of pulmonary tuberculosis, but evidence (as of March 2012) for using Xpert MTB/RIF for diagnosing extra pulmonary tuberculosis is still comparatively weak Globally, there is still a dearth of studies involving the use of Xpert MTB/RIF in extra pulmonary tuberculosis specimens, and few provide definitive answers. This is due mostly to the studies having small sample sizes across a range of various specimen types and differences in pre-processing methodologies and in input volumes and to studies having been conducted in different populations (adults, children, Human immunodeficiency virus infected).