Detection of Mycobacterium tuberculosis from paraffin-embedded tissues by INNO-LiPA Rif.TB assay: Retrospective analyses of Health Protection Agency National Mycobacterium Reference Laboratory data

Molecular diagnostic methods are of potential value in identifying tuberculosis (TB) and drug resistance where tissue specimens have been submitted for histology but not for microbiological culture. All paraffin-embedded tissue (PET) specimens (n=60) referred to a single national centre over a 42 month study period were analysed using the INNO-LiPA Rif.TB assay; 29/60 patients had been reported to the UK Enhanced Tuberculosis Surveillance database with a diagnosis of TB based on clinical, radiological and histological evidence. Mycobacterium tuberculosis (MTB) DNA was detectable in 5 out of 29 reported TB cases (17.2 %); 12 out of 29 of the reported TB cases had a positive MTB culture from a secondary clinical specimen and MTB DNA was detectable in 2 of the 12 (16.7%) laboratory-confirmed TB cases. Referring clinicians should be aware of the limitations of this assay on PETs, and should request molecular testing only in patients with a high clinical probability of TB and when acid-fast bacilli are seen in tissue specimens.