Other CBNAAT tests - Availability and Utility

Introduction

Cartridge-based Nucleic Acid Amplification Test (CBNAAT) is an automated rapid molecular diagnostic test which detects targeted Deoxyribonucleic Acids (DNA) sequences of Mycobacterium tuberculosis (M.tb) genome by Real-time Polymerase Chain Reaction (RT-PCR) method.

CBNAAT uses the GeneXpert IV Dx system and the single-use disposable Xpert M.tb/ Rifampicin (RIF) cartridges that hold the Polymerase Chain Reaction (PCR) reagents and host the PCR process.

The various TB tests utilizing the CBNAAT platform:

1) GeneXpert MTB/ RIF

• The Xpert M.tb/ RIF assay is a Nucleic Acid Amplification Test (NAAT) that uses a disposable cartridge with the GeneXpert Instrument System to quickly identify possible Multidrug-resistant TB (MDR-TB) that is resistant to RIF.
• This test yields rapid results, i.e., within 2 hours and is therefore cost and time-saving.

2) GeneXpert MTB/ RIF Ultra 

• The Xpert M.tb/ RIF Ultra assay is similar to the Xpert MTB/ RIF assay, just that it is even faster with a higher level of accuracy.
• The results are obtained in 80 minutes.
• It can detect paucibacillary TB disease.

3) GeneXpert MTB/ XDR

• This is a GeneXpert M.tb assay that detects mutations associated with Resistance Towards Isoniazid (INH), Fluoroquinolones (FLQ), Second Line Injectable Drug (SLID) (amikacin, kanamycin, capreomycin) and Ethionamide (ETH) in a single test.

4) GeneXpert Omni/Edge

• GeneXpert Omni/Edge is a battery-operated, wireless and web-enabled portable molecular diagnostics system, intended for use as the point-of-care diagnostic tool in remote and challenging settings.
• It is a single-slot platform i.e., runs one test per cycle, uses a 2-in-1 tablet/laptop and a compact printer and is expected to enable accurate, fast and cost effective test results.

Apart from TB, the CBNAAT platform can be used to diagnose several other pathogens using different cartridges. One of the common other pathogens detected using CBNAAT in India is COVID-19.

Note: Except GeneXpert MTB/ RIF , other CBNAAT tests are not currently being endorsed by NTEP.

Resources

• WHO Consolidated Guidelines on Tuberculosis. Module 3: Diagnosis - Rapid Diagnostics for Tuberculosis Detection 2021 Update.
• Guidelines for Programmatic Management of Drug-resistant TB (PMDT) in India; NTEP, CTD, MoHFW, India, 2021.
• Sachdeva K, Shrivastava T. CBNAAT: A Boon for Early Diagnosis of Tuberculosis-Head and Neck; Indian J Otolaryngol Head Neck Surg, 2018.

Assessment