Pleural fluid beta-2-microglobulin and angiotensin-converting enzyme concentrations in rheumatoid arthritis and tuberculosis.

Concentrations of beta 2-microglobulin (B2M) and angiotensin-converting enzyme (ACE) were measured in pleural fluid (Pf) and serum (S) of 364 patients with pleural effusions. Eleven patients had rheumatoid arthritis (RA), 36 verified tuberculosis (TB), 15 suspected TB, 120 cancer, 21 empyema, 34 pneumonia, 33 various defined diseases, 67 effusions of unknown aetiology and 27 congestive heart failure. The median concentrations of Pf-B2M and Pf-ACE were significantly higher in patients with RA than in patients with any other disease (p < 0.005). Tuberculous effusions contained higher Pf-ACE concentrations than any other type of non-rheumatoid effusion (p < 0.05). With sensitivities of 91%, the specificity of Pf-B2M and Pf-ACE for the diagnosis of RA was 86% and 55%, respectively. Local cellular immune events probably account for the abundance of B2M and ACE in rheumatoid and tuberculous pleural effusions. Pf-B2M and Pf-ACE determinations may aid in the differentiation of rheumatoid and tuberculous pleurisy from other types of pleural disease.