The finding of a predominantly PMNL exudate should not rule out TPE, particularly when pleural ADA activity is elevated. The collection of sputum and pleural fluid samples for mycobacterial culture should be encouraged in the case of suspected PMNL-rich TPE, as they are frequently positive in this early stage.

An automated nucleic acid amplification assay that simultaneously identifies Mycobacterium tuberculosis and rifampicin resistance, the Xpert® MTB/RIF test, has undergone extensive evaluation in sputum samples. Our aim was to define its diagnostic accuracy when performed on pleural fluid specimens. In 67 patients with pleural effusions, of whom half had tuberculous pleuritis, Xpert yielded 15% sensitivity and 100% specificity in the detection of tuberculosis (TB). Positive Xpert results tended to be more common in patients with microbiologically confirmed TB. Due to its low sensitivity, Xpert testing of pleural fluids has a limited role in the work-up of pleural effusions.

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In this retrospective study of 80 pleural effusions, the combination of thyroid transcription factor 1 (TTF-1) and napsin A immunostaining on fluid cell blocks was positive in 80% of lung adenocarcinomas. Although measuring TTF-1 pleural fluid concentrations was of no value, quantification of napsin A levels allowed the identification of one third of the double-negative stained lung adenocarcinomas, with an overall accuracy similar to classical tumour markers for malignant-benign discrimination (sensitivity 40%, specificity 100%).