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Interferon-gamma assays in TB diagnosis
P19 GeneXpert MTB.Rif assay improves the diagnostic yield of EBUS-TBNA in smear-negative intra-thoracic tuberculous lymphadenopathy
  1. D J Dhasmana1,
  2. C J Bradley1,
  3. P George1,
  4. D W Connell2,
  5. P Molyneaux1,
  6. A Singanayagam1,
  7. A Lalvani2,
  8. A Jepson1,
  9. O M Kon1,
  10. G S Cooke3
  1. 1St Mary's Hospital, Imperial College Healthcare Trust, London, UK
  2. 2Tuberculosis Research Unit, Department of Respiratory Medicine, National Heart and Lung Institute, Imperial College London, London, UK
  3. 3Division of Infectious Diseases, Department of Medicine, Imperial College London, London, UK

Abstract

Introduction and Objectives Tuberculosis notifications in the UK continue to rise and the diagnosis of both disease and drug resistance can be challenging. Endobronchial ultrasound (EBUS) and EBUS-guided transbronchial nodal aspirates (TBNA) have been shown recently to be a safe and effective tool in the diagnosis of intra-thoracic TB lymphadenopathy. New molecular techniques, notably the GeneXpert MTB.Rif system (Cepheid) have shown great promise in the diagnosis of pulmonary disease but have not been evaluated in intra-thoracic nodal disease.

Methods As part of an ongoing study, consecutive patients with intra-thoracic lymphadenopathy were prospectively studied within our tertiary EBUS service between January 2010 and March 2011. In addition to standard cytological and microbiological investigations, a single GeneXpert MTB.Rif assay was performed on EBUS-TBNA samples. Using established methods, a final diagnosis was given of definite/highly probable TB, possible TB or not TB/alternative diagnosis. Performance of the GeneXpert MTB.Rif assay was then evaluated in the context of these final diagnoses.

Results 74 patients (3 HIV-positive) underwent EBUS-TBNA sampling. Nineteen have been diagnosed with definite/highly probable TB to date. A single GeneXpert assay had a sensitivity of 67% (8/12) from culture-positive TBNA. 11/15 (73%) of patients with a positive culture from any tissue and 13/19 (68%) patients classed as definite/highly probable TB had positive GeneXpert results. One case of confirmed MDR-TB was correctly identified and treatment started promptly. Fifteen patients had positive GeneXpert MTB.Rif results from EBUS-TBNA: 13/15 were given immediate TB treatment. One of the remaining two cases without strong microbiological or cytological findings was subsequently diagnosed with active tuberculosis supported by evidence of PET-positive mediastinal lymph nodes. The other case appears not to have active disease and remains under follow-up.

Conclusions A single GeneXpert MTB.Rif assay has good sensitivity in the context of culture-positive intra-thoracic tuberculous lymphadenopathy and can provide an immediate diagnosis of likely MDR-TB. Positive PCR results were seen in two patients where conventional techniques were inconclusive and in one provided the main support for the diagnosis. These results suggest the addition of the GeneXpert MTB.Rif assay to the investigation of intra-thoracic nodal disease improves diagnostic yield.

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