Originally Posted by
Doc Alan
The chest X-ray is the main test for TB, but not the only one. It’s necessary to have a full clinical history and examination by the doctor at the test centre, as TB may not just affect the lungs. The doctor needs to know if you have been vaccinated ( BCG ; which doesn’t guarantee 100% protection ), and may require a skin test ( Mantoux ). Blood tests ( IGRA / Xpert MTB/RIF test ) are also becoming available, which might be used instead of ( or as well as ) sputum tests, to give a more rapid diagnosis.
If there are symptoms such as coughing with sputum production, then sputum sample(s) do need to be tested.
The sample(s) are examined under the microscope for the TB bug ( Mycobacterium tuberculosis ). This needs a special stain ( Ziehl-Neelsen ) ; but even if someone has TB, the bugs can be very elusive to see. Negative direct microscopy doesn’t rule out TB.
The sputum needs to be “ cultured “ to allow any TB bugs to grow. Unfortunately they grow slowly, so it takes several weeks before they can be examined. “ Ten weeks “ – as you were told – is the maximum time ( six weeks would be more usual ). If positive, it could then take a further month or so to make sure which antibiotics to use. ( If there were clinical signs of TB, treatment could be started before the culture results ).
If, as expected in your case, culture for TB bugs is negative, and you have no symptoms, with a normal original chest X-ray, I wouldn’t expect a further X-ray would be necessary. The decision would, however, be up to the doctor at the centre.