Mycobacterium and TB PCR (afb aafb mycobacteria tuberculosis)

Microbiology

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

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.

Transport to the laboratory immediately. Refrigerate samples if transport is delayed.

Sent to a National Reference Centre

Up to 3 working days