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Diagnostic evaluation of pleural effusion in adults: Additional tests for undetermined etiology

YC Gary Lee, MBChB, PhD
Section Editor
V Courtney Broaddus, MD
Deputy Editor
Geraldine Finlay, MD


Pleural effusions can develop as a result of over 50 different pleuropulmonary or systemic disorders. Following diagnostic thoracentesis, the cause of a pleural effusion is not evident in up to 25 percent of patients [1,2]. However, no universally accepted definition exists for an "undiagnosed effusion."

This topic will review the approach to pleural effusions for which the diagnosis is unclear after initial clinical assessment and investigation. The initial assessment of a patient with a pleural effusion is presented separately. (See "Imaging of pleural effusions in adults" and "Diagnostic evaluation of a pleural effusion in adults: Initial testing" and "Diagnostic thoracentesis".)


The first step for the clinician is to revisit the patient's history, paying particular attention to drugs, occupational exposures, risk factors for pulmonary embolism or tuberculosis, and comorbid conditions.

A careful drug history may reveal that the patient is taking nitrofurantoin, amiodarone, ovarian stimulation therapy, or a drug that can produce a lupus-like syndrome [3,4]. (See "Drug-induced lupus".)

Occupational asbestos exposure, which might suggest a benign asbestos pleural effusion, may have occurred many years earlier [5]. Benign asbestos effusions are usually unilateral, exudative, and about a third have an elevated pleural eosinophil count [6].

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Literature review current through: Nov 2017. | This topic last updated: Jun 13, 2016.
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