Mycobacterium tuberculosis PCR (Fine Needle Aspirate)

Diagnostic Use

PCR detects MTB complex (which includes M.tuberculosis and M.bovis)

IMPORTANT NOTE – Please read:

Because of the difficulty in defining a “gold standard” of diagnosis for tuberculosis in many cases, the sensitivity and specificity of PCR for each specimen type has not been validated and will depend on a number of factors, including volume of specimen. However, local experience with the test suggests sensitivity to be about 50%, whereas overall specificity is 95% or more when compared to clinical diagnosis and culture.

PCR for M. tuberculosis DNA will have most value when the possibility of infection is high and much less if used as a “screening test”. The value of the test performed on CSF with < 5 white blood cells is very doubtful and requires prior discussion with a clinical microbiologist (see below).

It is essential that microscopy and culture for mycobacteria also be requested as PCR-negative, culture-positive results may be obtained. In addition, culture will allow susceptibility tests to be performed.

A positive PCR result for M. tuberculosis is highly significant; a negative PCR result does not exclude infection.