NAAT for the detection of active mycobacterial infection is intended to be used in patients suspected of having TB or NTM infections to confirm the presence of the organism and help direct patient management. NAAT to detect MTB will be a separate test from NAAT to detect NTM infections and will require two MBS item numbers.
Nucleic acid amplification test (NAAT)
NAAT can be undertaken using either an in-house (diagnostic laboratory-designed) method or a commercial assay. The methods used for in-house NAAT are usually polymerase chain reaction (PCR)-based, where DNA is amplified via a temperature-mediated DNA polymerase using specific primers complementary to the ends of the targeted sequence. The most widely used commercial NAAT for detection of MTB is the GeneXpert MTB/RIF assay (Xpert, Cepheid, Sunnyvale, CA, USA), which is endorsed by the World Health Organization and has been approved by the Therapeutic Goods Administration (TGA) for use on patient material, regardless of the AFB smear microscopy result. There are no commercially available kits for the detection of NTM approved by the TGA in Australia.
The Guidelines for Australian mycobacteriology laboratories (National Tuberculosis Advisory Committee 2006) state that ‘All NAAT methods must be properly validated before routine use’. Commercial tests that have been modified (e.g. for a novel use) and in-house methodologies must be validated according to the NPAAC guidelines for requirements for the development and use of in-house in-vitro diagnostic medical devices (National Pathology Accreditation Advisory Council 2014).
