Use of Lateral Flow pleural fluid Lipoarabinomannan assay on the differential diagnosis of pleural tuberculosis.

Pleural tuberculosis (PlTB) is the commonest extrapulmonary presentation of the disease, showing a paucibacillary manifestation and presenting a compartmentalized immune response, which adds difficulties to its diagnosis. The Lateral-Flow Lipoarabinomannan assay (LF-LAM) is a rapid diagnostic tool based on the detection of mycobacterial LAM antigen in urine, standardized as a point-of-care for TB-HIV co-infection diagnosis. We aimed to investigate the potential use of LF-LAM assay in pleural fluid (PF) samples from patients with pleural effusion due to PlTB and other diagnoses. A retrospective study was conducted using PF samples, stored at -80°C in a biorepository, from patients with non-HIV PlTB and other non-TB diagnoses, recruited from Pedro Ernesto University Hospital, Rio de Janeiro State University, Rio de Janeiro, Brazil. PF samples were defrosted and then applied to the LF-LAM. The performance of the test was compared to smear microscopy, mycobacterial culture, rapid molecular test, histopathology, and adenosine deaminase (ADA) levels. A total of 101 pleural fluid samples were subjected to LF-LAM: 55 non-TB and 46 PlTB. A third of PF from PlTB group have shown a positive reaction (Sensitivity = 33%), while non-TB group were all negatives (Specificity = 100%). Rapid molecular test, histopathology and ADA showed sensitivity of 7.1%, 66.7% and 86.4%, respectively. Although preliminary, our study found out an interesting performance of the LF-LAM assay in an unusual sample, such as PF, and may contribute to improve the differential diagnosis of PlTB among pleural effusion patients under investigation, which allow a rapid initiation of the anti-TB treatment.