Tests based on polymerase chain reactions are increasingly important in the microbiological diagnosis of tuberculosis (TB). Park et al1 have extended the use of Xpert Ultra to include material obtained at bronchoscopy, and particularly its use for samples obtained by endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA). In addition, immediate cytology with rapid onsite evaluation contributed significantly to the differential diagnosis of enlarged mediastinal lymph node (MLN) disease. A review panel of the results in combination with clinical features was an important element of the study.

In 2010, the WHO recommended that nucleic acid amplification tests (NAATs) be used to identify Mycobacterium tuberculosis (Mtb) in pulmonary and extrapulmonary TB.2 A Cochrane review noted that Xpert Ultra was better than Xpert MTB/RIF in the diagnosis of TB meningitis.3 However, aspirates from MLNs were not included in either analysis. One previous study has investigated the role of EBUS-TBNA and presented data with a diagnosis based on a combination of Xpert MTB/RIF, a positive tuberculin skin test and heterogeneity in the ultrasound texture of the MLN(s) with or without central necrosis.4

The scientific basis underlying these NAATs will help understand their benefits and potential problems, as well as clarify areas …