Beta 2 microglobulin in pleural effusions.

Beta 2 microglobulin (beta 2m) concentrations in serum and pleural fluid from 64 patients with pleural effusion were studied. The level of beta 2m in pleural fluid was generally twice that in serum. The ratio of pleural fluid beta 2m to serum beta 2m in patients groups defined according to the final diagnosis showed an interestingly high value in tuberculous pleuritis and in patients with rheumatoid arthritis with pleural effusion. There was a positive correlation between the beta 2m and lysozyme contents in pleural fluid, suggesting local and simultaneous activation of different cell lines when the pleura is involved. We suggest that pleural fluid and concomitant serum beta 2m measurements should be taken into consideration when pleural effusion of tuberculous origin is suspected. Furthermore, beta 2m determination might help to differentiate between rheumatoid pleural fluid and pleural involvement due to the other systemic diseases.