Cepheid, the manufacturer of the Genexpert test, has now developed a series of molecular tests for tuberculosis and other diseases based on the cartridge/assay used. The Genexpert can screen for a variety of infectious diseases, including tuberculosis and communicable diseases.
What exactly is the CB-NAAT?
The Genexpert is known as the CB-NAAT in India. The Cartridge Based Nucleic Acid Amplification Test is the full name of the CB-NAAT test.
How does the Genexpert test for tuberculosis?
The Genexpert detects the presence of TB bacteria to diagnose tuberculosis. The test is a molecular TB test that detects DNA in tuberculosis bacteria. It works with a sputum sample and can provide results in less than 2 hours.
The Genexpert can also detect genetic mutations associated with Rifampicin resistance.
How much does the Genexpert TB test cost?
FIND initially negotiated discounts for the Genexpert test in 120 high burden countries as well as all low and middle income countries, and the initial cost was around US$17 per cartridge.
UNITAID approved $30 million in funding in June 2012 with the goal of expanding access to the Genexpert test. It was hoped that the test’s implementation would reduce the price from US$17 to US$10. However, the roll out was slower than expected, and many customers are believed to have delayed ordering because they expected the price to be reduced following the UNITAID announcement.
- Machine with GeneXpert 4 modules
- Machine with GeneXpert 4 modules
The application of the Genexpert test
The WHO recommended that the test be used as the first line of defence in people suspected of having MDR TB or HIV-associated TB. They also suggested that, due to the lack of accuracy of smear microscopy, it could be used as a follow-up test to microscopy in settings where MDR TB and/or HIV are of less concern, particularly in smear negative specimens. They did, however, acknowledge the significant resource implications of using it in this second manner. 4
The WHO also stressed that the test does not replace traditional microscopy culture and drug sensitivity testing, which are still required to monitor treatment progress and detect other types of drug resistance.
Disadvantages
The disadvantages are as follows:
- The cartridges have an 18-month shelf life.
- A very stable power supply is required.
- The instrument must be calibrated once a year.
- The price of the test;
- The temperature limit is crucial.8
Advantages
The main benefits of the test for diagnosis are its reliability when compared to sputum microscopy and its speed of results when compared to the culture test. Although sputum microscopy is quick and inexpensive for diagnosing tuberculosis, it is frequently unreliable. It is especially untrustworthy when people are HIV positive. Although culture provides a definitive diagnosis, the process usually takes weeks rather than the hours required by the Genexpert test.