Background: Pleural effusion secondary to a nonmalignant cause can represent significant morbidity and mortality. Nonmalignant pleural effusion (NMPE) is common, with congestive heart failure representing the leading cause. Despite this, there are limited data on mortality risk and associated prognostic factors.

Methods: We recruited 782 consecutive patients presenting to a pleural service between March 2008 and March 2015 with an undiagnosed pleural effusion. Further analysis was conducted in 356 patients with NMPE. Pleural biochemical analysis, cytologic analysis, thoracic ultrasonography, and chest radiography were performed. Echocardiography, CT imaging, radiologically guided biopsy, and medical thoracoscopy were undertaken as clinically indicated. Patients were followed for a minimum duration of 12 months, with the final diagnosis decided through independent review by two respiratory consultants.

Results: Of the 782 patients, 356 were diagnosed with NMPE (46%). These patients had a mean age of 68 years (SD, 17 years) with 69% of them being men. Patients with cardiac, renal, and hepatic failure had 1-year mortality rates of 50%, 46%, and 25%, respectively. Bilateral effusions (hazard ratio [HR], 3.55; 95% CI, 2.22-5.68) and transudative effusions (HR, 2.78; 95% CI, 1.81-4.28) were associated with a worse prognosis in patients with NMPE, with a 57% and 43% 1-year mortality rate, respectively.

Conclusions: This is the largest prospectively collected series in patients with NMPE, demonstrating that cases secondary to organ dysfunction have extremely high 1-year mortality. In addition, the presence of bilateral and transudative effusions is an indicator of increased mortality. Clinicians should be aware of these poor prognostic features and guide management accordingly.