GENXPERT: WHAT, WHEN AND HOW?

What is Genexpert TB Test?

• The Xpert MTB/RIF detects DNA sequences specific for Mycobacterium tuberculosis and Rifampicin resistance by polymerase chain reaction
• It is based on the Cepheid GeneXpert system, a platform for rapid and simple-to-use nucleic acid amplification tests (NAAT
• The Xpert® MTB/RIF purifies and concentrates Mycobacterium tuberculosis bacilliform sputum samples, isolates genomic material from the captured bacteria by sonication and subsequently amplifies the genomic DNA by PCR
• The process identifies all the clinically relevant Rifampicin resistance inducing mutations in the RNA polymerase beta(rpoB) gene in the Mycobacterium tuberculosis genome
• Results are obtained from unprocessed sputum samples in 90 minutes
  It has a sensitivity of 89% and specificity of 99%

Advantages of the GeneXpert TB test:

• The test can be done on AFB smear positive and AFB smear negative samples
• The test can be done on pulmonary and extra pulmonary samples
• The results are available the same day
• The specificity of the test is 99%, so very few false positive cases
• The test detects Rifampicin resistance (rpoB gene) which is the surrogate maker for MDRTB

Utility of the GeneXpert test:

GeneXpert is recommended forrapid and confirmatory molecular diagnosis of tuberculosis

• Prevents delays in diagnosis and treatment initiation
• Detects Rifampicin resistance (detects rpoBgene mutation)
• Helps in selecting the most appropriate antitubercular drugs
• Can be performed on all samples: pulmonary & extra pulmonary, smear positive or negative
• Highly sensitive (88%) and specific (98%)
• Recommended as an early confirmatory test by WHO for suspected MDRTBand HIV-TBco-infection