Comparison of the GeneXpert® MTB/RIF Test and Conventional Methods in the Diagnosis of Mycobacterium tuberculosis

Abstract

Background: The objective of this study is to evaluate the performance of the GeneXpert MTB/RIF system in Mycobacterium tuberculosis (MTB) diagnosis and the detection of rifampicin resistance in pulmonary and extrapulmonary clinical samples.

Methods: A total of 849 samples (611 pulmonary and 238 extrapulmonary), which were sent to the laboratory of our hospital on suspicion of MTB, were included in the study. The samples cultured on Lowenstein Jensen medium and Mycobacteria Growth Indicator Tubes. All samples were also tested with the GeneXpert MTB/RIF test. The drug susceptibility test was determined using the Bactec MGIT 960 system.

Results: MTB grew in the culture in 84 (9.8%) of all samples, and 78 (9.1%) were found to be positive by the GeneXpert MTB/RIF test, while acid-fast bacillus (AFB), MTB/RIF test, and culture positivity were 41 (6.7%), 74 (12.1%), and 75 (12.3%), respectively, in pulmonary samples, and these values were found to be 2 (0.8%), 4 (1.7%), and 9 (3.8%), respectively, in extrapulmonary samples. In the automated culture and susceptibility system, rifampicin resistance was detected in only one of 84 (2.6%) isolated strains. This resistant strain was also identified by the GeneXpert MTB/RIF test. According to the culture results of all samples examined, the sensitivity of the GeneXpert MTB/RIF test was calculated as 83.3%, specificity as 98.9%, PPV as 89.7%, and NPV as 98.1%.

Conclusions: The GeneXpert MTB/RIF test used in the study was found to be highly successful, very quick, and requiring low workload in pulmonary samples and extrapulmonary samples in terms of sensitivity and specificity. It was observed that it can be used safely due to its high sensitivity, especially in AFB-positive samples.