Finding the right tests…
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Emergency services available 24 x 7
Finding the right tests…
Molecular
AFB rapid culture on the BacT/ALERT 3D system looks for Mycobacterium tuberculosis and related mycobacteria by growing them in a sealed liquid broth bottle instead of the traditional solid, egg-based medium. A machine monitors the bottle continuously for signs that bacteria are multiplying, rather than waiting for someone to check a plate by eye every few days. This liquid method picks up more true positive cases than older solid media and flags growth sooner, though it remains a culture at heart - the bacteria still need to multiply to detectable numbers, so it takes noticeably longer than a PCR-based test like GeneXpert. A positive bottle confirms a living organism your doctor can test against TB drugs directly.
This test reports whether mycobacteria grew from your sputum sample during the observation period, then flags a positive bottle for species identification and drug susceptibility testing. A positive result strongly suggests active tuberculosis or another mycobacterial infection, though confirming exactly which species is a separate follow-up step. A negative result means nothing grew from your sample in the time the system monitored it - reassuring, but not a complete rule-out, especially if the sample had very few organisms in it or was collected poorly.
Traditional TB culture uses Lowenstein-Jensen medium, a solid, egg-based slant a technician checks by eye every few days for tiny colonies. The BacT/ALERT 3D system instead grows your sample in a liquid broth inside a sealed bottle, and sensors track the gas mycobacteria produce as they multiply. A study comparing the two methods across more than 1,600 specimens found the liquid system detected meaningfully more positive cases and flagged growth in roughly half the time solid culture needed.
A PCR-based test such as GeneXpert reads the bacteria's genetic material directly, so it doesn't need anything to grow - that's why it returns an answer far sooner. Culture instead depends on live bacteria multiplying to a level sensors can detect, which is inherently slower but proves the organism is alive, not just present as leftover DNA.
Once a bottle flags positive, the lab still needs to confirm which mycobacterial species is growing and run drug susceptibility testing against first-line TB medicines. This is why culture remains valuable even after a molecular test - it's currently the reference method for checking whether TB bacteria actually respond to specific drugs.
Doctors often send AFB smear, a PCR-based test, and this culture from the same sputum sample together, since each answers a different question about whether TB is present and how to treat it.
GeneXpert reads the bacteria's genetic material directly from your sample, so it can give an answer without anything growing. This culture instead needs live mycobacteria to actually multiply in the liquid broth, which takes longer but confirms the organism is alive and lets the lab test it against TB drugs.
Culture depends on bacteria multiplying to a level the system's sensors can detect, and mycobacteria grow slowly compared to most other bacteria. A PCR test skips that step entirely by detecting genetic material directly, which is why it returns a result much sooner.
A positive bottle means mycobacteria grew from your sputum sample, which strongly suggests active TB or a related infection. The lab then identifies the exact species and can test the organism against TB medicines to guide your treatment.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Not by itself. Once bacteria grow in the bottle, the lab runs a separate drug susceptibility test on the live organism, which is the main reason culture is still used even when faster molecular tests are available.
It means no mycobacteria grew from your sample in the time the system monitored it. This is reassuring but not a complete rule-out, particularly if the sputum sample contained very few organisms or wasn't collected well.
Liquid culture systems like BacT/ALERT 3D pick up more true positive TB cases and flag growth sooner than the traditional solid, egg-based medium, based on studies comparing the two methods side by side.