The value of pleural fluid anti-A60 IgM in BCG-vaccinated tuberculous pleurisy patients

Objectives   To determine if detection of IgM and IgG antibodies against mycobacterial antigen A60, together with the Mantoux tuberculin skin test (TST), could be used in the diagnosis of tuberculous pleurisy (TP) in BCG-vaccinated cases.
Methods   We investigated 125 BCG-vaccinated patients with pleural effusion. Of these, 88 had TP and 37 had non-tuberculous pleurisy (NTP). TST and anti-A60 IgM and IgG measurements by ELISA were performed in the sera and pleural effusions of both groups.
Results   Cut-off values, in optical density, for serum anti-A60 IgM, pleural fluid anti-A60 IgM, serum anti-A60 IgG and pleural fluid anti-A60 IgG were defined as 0.624, 0.614, 0.464, and 0.613, respectively. TP patients had higher IgG and IgM levels in the serum ( P  < 0.001 and P  < 0.05, respectively) and pleural effusion ( P  < 0.001 and P  < 0.001, respectively). Regardless of the diagnosis, IgG and IgM levels were higher in the sera ( P  < 0.001 and P  < 0.05, respectively) and pleural effusions ( P  < 0.001 and P  < 0.001, respectively) of TST-positive cases, and serum and pleural fluid IgM levels were higher ( P  < 0.001 and P  < 0.001, respectively) in the TST-positive TP cases. Sensitivity and specificity of TST were 65% and 68%, respectively. As a single parameter, pleural fluid anti-A60 IgM had the highest sensitivity (77%) and specificity (94%) in patients with negative TST.
Conclusion   We suggest that in populations where tuberculosis prevalence is high and BCG vaccination is common, pleural fluid anti-A60 IgM can facilitate the diagnosis of TP.