GeneXpert
GeneXpert is a rapid molecular test that reads the bacterium's genetic fingerprint rather than waiting to see it grow. A sputum sample is loaded into a sealed cartridge, slotted into the machine, and within about two hours it answers two questions at once: is TB DNA present, and does the bacterium carry resistance to rifampicin, a key TB drug?
Its power lies in speed and simplicity. Because it amplifies and detects specific stretches of TB DNA, it is far more sensitive than smear microscopy and can find infection that the microscope misses. The automated, cartridge-based design needs little laboratory training, which has helped push fast, accurate TB diagnosis into clinics far from major reference labs.
Rifampicin resistance is used as a warning flag for multidrug-resistant TB, because resistance to rifampicin usually travels with resistance to other first-line drugs. The test is not perfect: it can stay positive after successful treatment (it detects DNA, including from dead bacteria), so it is not used to monitor response, and resistance results sometimes need confirmation.
A patient's sputum is run on GeneXpert; within hours it reports TB detected with rifampicin resistance, prompting a switch to a drug-resistant treatment regimen.
TB diagnosis and resistance screen in a single rapid step.
GeneXpert is a brand of nucleic acid amplification test (NAAT); the original TB cartridge is called Xpert MTB/RIF, where “RIF” refers to the rifampicin-resistance result.