Characteristics of pleural effusions in systemic lupus erythematosus: differential diagnosis of lupus pleuritis.

We investigated the clinical characteristics of pleural effusion in systemic lupus erythematosus (SLE). A prospective analysis of 17 SLE patients with pleural effusion (seven lupus pleuritis, eight transudative effusions and two parapneumonic effusions) was performed. Thirty non-SLE patients with pleural effusion were recruited as controls. A pleural fluid ANA titer ≥1:160 was found in 8/17 (47.1%) SLE patients and none of the 30 non-SLE patients (p = 0.0001). Pleural fluid to serum C3 ratios were significantly lower in SLE than in non-SLE (median (minimum-maximum) 0.29 (0.03-0.43) versus 0.52 (0.26-0.73), p = 0.0002). Among SLE patients, pleural fluid ANA titers ≥1:160 were more frequently found in patients with lupus pleuritis than in those with pleural effusion from causes other than lupus itself (85.7% versus 20.0%, p = 0.0152). Serum CRP levels were significantly increased in patients with lupus pleuritis compared with SLE patients with transudative pleural effusion (2.30 (0.30-5.66) versus 0.7 (0.12-1.47) mg/dl, p = 0.0062). In conclusion, pleural fluid ANA titer and serum CRP levels are significantly increased in lupus pleuritis.