Etiology of pleural effusions: analysis of more than 3,000 consecutive thoracenteses

Objective: To investigate the etiology of pleural effusions (PE) in adults and the accuracy of pleural fluid (PF) cytology and cultures in malignant and infectious PE, respectively.

Patients and methods: Retrospective analysis of all consecutive patients with PE undergoing diagnostic thoracentesis during the last 19 years in a university hospital.

Results: The leading causes of PE among the 3,077 patients were: cancer (27%), heart failure (21%), pneumonia (19%), tuberculosis (9%), abdominal surgery (4%), pericardial diseases (4%) and cirrhosis (3%). Tuberculosis was the most common etiology in patients <34 years of age (52%), whereas heart failure predominated in octogenarians (45%). The most common primary tumors in malignant PE were lung (37%) and breast (16%). The overall accuracy of PF cytology was 59%, although it was significantly lower in mesotheliomas (27%) and squamous cell lung cancer (25%). In infectious PE, only 30% of cultures yielded positive results, a percentage which increased two-fold (66%) in purulent fluids (empyemas). Viridans streptococci were the most commonly isolated pathogens (25.5%). The sensitivity of solid media cultures of PF for Mycobacterium tuberculosis was low (18.5%).

Conclusions: Three-quarters of patients with PE in whom a diagnostic thoracentesis was indicated had cancer, heart failure, pneumonia or tuberculosis. PF cytology and cultures give false negative results in a significant number of cases.