Clinical Approach to a Pleural Effusion.

Determining the cause of a pleural effusion remains clinically challenging. Pleural fluid analysis (PFA) is an essential component of the diagnostic approach that we have reviewed in detail in a companion paper. However, despite the importance of PFA in establishing the cause of a pleural effusion, pathognomonic pleural fluid findings are rare. The true diagnostic value of PFA lies in its integration with the broader clinical picture. This diagnostic approach requires a systematic evaluation combining PFA with medical history, physical examination, laboratory data, and radiographic studies. In this manuscript, we review clinical features beyond PFA that are important in determining the cause of a pleural effusion. A detailed medical history may reveal important comorbidities, exposures, and previous surgical procedures that have diagnostic relevance. Radiographic findings, including the anatomic locations of pleural fluid, radiographic features, and the chronicity of the effusion, also may be diagnostically important. Blood tests may supply additional diagnostic information. Underpinning this diagnostic approach is that the clinician requires a deep understanding of the breadth of pleural diseases and their associated clinical presentations.