Performance of the Xpert MTB/RIF assay in the diagnosis of tuberculosis in formalin-fixed, paraffin-embedded tissues

Int J Mycobacteriol. Jan-Mar 2017;6(1):87-93. doi: 10.4103/2212-5531.201892.

Abstract

Objective/background: Extrapulmonary tuberculosis (EPTB), which accounts for 10%-40% of the global burden of TB, with the highest incidence in Sub-Saharan Africa, is strongly associated with human immunodeficiency virus infection. Diagnosing EPTB is challenging, and recently, there has been a concerted effort to evaluate the latest molecular diagnostics for diagnosing TB in a range of specimen types. The Xpert MTB/RIF assay (Cepheid, Sunnyvale, CA, USA) is one such technology, which simultaneously detects Mycobacterium tuberculosis and rifampicin resistance. Our objective was to evaluate the accuracy of the Xpert MTB/RIF assay for the diagnosis of EPTB and detection of rifampicin resistance in routinely processed formalin-fixed, paraffin-embedded (FFPE) tissues, compared with histological detection of TB as the gold standard.

Methods: A convenience set of 100 biobanked FFPE tissues, including lymph nodes (n = 64), male genital tract tissue (n = 10), abdominal tissue (n = 8), female genital tissue (n = 5), breast tissue (n = 5), synovial tissue (n = 4), skin (n = 2), tongue tissue (n = 1), and thyroid (n = 1), from routine cases of clinically suspected EPTB admitted to the University Teaching Hospital, Lusaka, Zambia, were analyzed using the Xpert MTB/RIF assay and in-house polymerase chain reaction (PCR) assay targeting IS6110, in parallel with Ziehl-Neelsen (ZN) staining, against histology as the gold standard.

Results: Some 66% of specimens had histological evidence of TB infection. ZN staining was positive for TB in 8% of cases, and Xpert MTB/RIF was positive for TB in 25% of cases. Taking histology as the gold standard, the sensitivity and specificity were as follows: In lymph tissue the accuracy of the Xpert MTB/RIF assay was 41% (95%CI 27-57), not significantly better than ZN or the in-house PCR assay. In non-lymph tissue the sensitivity of the in-house PCR assay was 82% (95%CI: 56%-95%), significantly higher than the Xpert MTB/RIF assay (P = 0.004). The Xpert MTB/RIF assay indicated rifampicin resistance in just three cases.

Conclusion: The Xpert MTB/RIF assay is potentially a useful tool for the diagnosis of TB in routine FFPE tissues.

Publication types

  • Evaluation Study

MeSH terms

  • Antibiotics, Antitubercular / pharmacology*
  • Diagnosis, Differential
  • Drug Resistance, Bacterial / genetics
  • Female
  • Formaldehyde
  • HIV Infections / complications
  • HIV Infections / microbiology
  • Histological Techniques
  • Humans
  • Lymph Nodes / microbiology
  • Male
  • Mycobacterium tuberculosis / drug effects*
  • Mycobacterium tuberculosis / genetics
  • Mycobacterium tuberculosis / isolation & purification*
  • Paraffin Embedding
  • Polymerase Chain Reaction*
  • Retrospective Studies
  • Rifampin / pharmacology*
  • Sensitivity and Specificity
  • Sputum / microbiology
  • Tissue Fixation
  • Tongue / microbiology
  • Tuberculosis / complications
  • Tuberculosis / diagnosis*
  • Tuberculosis / microbiology
  • Tuberculosis, Male Genital / diagnosis
  • Tuberculosis, Male Genital / microbiology
  • Tuberculosis, Multidrug-Resistant / diagnosis*
  • Tuberculosis, Multidrug-Resistant / microbiology
  • Tuberculosis, Pulmonary / diagnosis

Substances

  • Antibiotics, Antitubercular
  • Formaldehyde
  • Rifampin