The role of genexpert in the diagnosis of mycobacterium tuberculosis

Abstract

Background: GeneXpert(GXP) is a novel integrated Cartridge based nucleic acid amplification test with an established role for rapid diagnosis of mycobacterium tuberculosis and detection of rifampicin resistance. Aim: To evaluate diagnostic accuracy of GXP in pulmonary and extrapulmonary tuberculosis(TB) cases. Methodology: A prospective study was conducted in 257 presumptive TB patients with data retrieved for GXP, acid fast bacilli smear, culture and drug susceptibility test(DST). Sensitivity, specificity, positive predictive value(PPV), negative predictive value(NPV)of GXP in diagnosis and determination of rifampicin resistance in pulmonary and extrapulmonary TB cases were calculated and compared with culture and DST results. Results: Our study included 132 pulmonary and 125 extrapulmonary cases. On the basis of clinicoradiological and microbiological correlation diagnosis of TB was confirmed in 104 pulmonary and 103 extrapulmonary cases. Out of total 104 pulmonary TB cases 73 were rifampicin sensitive and 31 were rifampicin resistant cases.103 extrapulmonary TB cases included 66 rifampicin sensitive and 37 rifampicin resistant cases. The sensitivity, specificity, PPV, NPV of GXP in diagnosis and detection of rifampicin resistance in pulmonary TB was 95%,93%,98%,84% and 96%,100%,100%,96% respectively. The sensitivity, specificity, PPV, NPV of GXP in diagnosis and detection of rifampicin resistance in extrapulmonary TB cases was 79%,86%,96%,47% and 97%,95%,97%,95% respectively. Conclusion: GXP results are superior to smear microscopy and comparable to culture with shorter turn-around time. We recommend using it in routine TB diagnosis as this will expedite management of patients with presumptive TB.