Mycobacterium and TB PCR (afb aafb mycobacteria tuberculosis)
Microbiology
Notes
This is a rapid molecular test for the detection of M. tuberculosis complex and rifampicin resistance
- Can be performed on a range of samples, both pulmonary and non-pulmonary
- It is generally only performed after discussion with the Consultant Microbiologist
- A negative result does not exclude the clinical possibility of TB infection, or infection with other Mycobacteria
Sample requirements
- The ideal specimens are AAFB smear-positive pulmonary samples
- In general fluid samples such as CSF, pleural fluid and ascites have much lower sensitivities; the minimum amount of CSF (not supernatant) that will be examined is 0.5ml. However submitting the largest possible volume of CSF and other fluids will increase the sensitivity.
- This test can also be used to confirm positive cultures and to detect the presence of the rifampicin resistance gene
- Paraffin waxed blocks can be examined but sensitivity is lower than that for fresh tissue. For paraffin wax blocks, the whole wax block must be sent together with a diagram/slide indicating the area where any AFB/granuloma were seen. The reference laboratory will return the block on completion of the test.
Required information
- Relevant clinical details
- Please provide details of any recent anti-tuberculosis treatment
- Please provide details of recent BCG vaccination
Storage/transport
Transport to the laboratory immediately. Refrigerate samples if transport is delayed.
Turnaround time
Sent to a National Reference Centre
Up to 3 working days