Nucleic Acid Amplification Tests [NAAT]

A nucleic acid test (NAT) is a technique used to detect a particular nucleic acid sequence. In general, a NAT is used to detect and identify a particular species or subspecies of an organism (e.g., a virus or bacteria that acts as a pathogen in blood, tissue or urine).

As the genetic material is usually present at a low level, many NATs include a step that amplifies the genetic material (i.e., makes many copies of it) – such NATs are called nucleic acid amplification tests (NAATs)

Three new nucleic acid amplification test (NAAT) classes are endorsed by the World Health Organisation (WHO):

1. Moderate complexity automated NAATs, recommended for the initial detection of TB and resistance to rifampicin and isoniazid, providing more options for early diagnosis of TB and rifampicin-resistant TB but also addressing an important gap in the rapid diagnosis of isoniazid-resistant and rifampicin-susceptible TB
2. Low complexity automated NAATs, recommended for the detection of resistance to isoniazid and second-line anti-TB agents, which will improve access to testing of resistance to fluoroquinolones at the peripheral level
3. High complexity reverse hybridization based NAATs, recommended for the detection of pyrazinamide resistance, representing the first molecular tests for resistance determination to this drug

With this, there are two NAAT-based technologies in the program i.e., GeneXpert and Truenat. As of 2020, approximately 1200 GeneXpert machines and 1500 Truenat machines have been installed in laboratories. India’s National TB Elimination Program (NTEP) has incorporated Truenat in its diagnostic algorithm and is scaling up diagnosis through them.

The NAAT laboratories do not require sophisticated biosafety level infrastructure for its functioning. Hence, any designated laboratory can be upgraded to a NAAT laboratory. It is the vision of the NTEP that universal drug susceptibility testing should be offered to all confirmed TB cases and hence NAAT laboratories are decentralised to the maximum extent possible. Currently, the program has NAAT laboratories both in the public and private sectors.