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Pleural effusion
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Pleural effusion

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Contributors: Paritosh Prasad MD, Ryan R. Walsh MD, Joshua J. Jarvis MD, Alastair Moore MD, Eric Ingerowski MD, FAAP
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A pleural effusion is increased fluid within the pleural cavity. Symptoms can include shortness of breath, cough, and pleuritic chest pain, although effusions are often asymptomatic and identified incidentally on chest radiology. Pleural effusions are most commonly caused by infection, congestive heart failure, malignancy, connective tissue disorders, liver disease, and trauma. Analysis of the fluid can help identify the responsible etiology.

Clinically, effusions may be categorized as either transudates or exudates. Thoracentesis and laboratory evaluation as well as radiographic characteristics distinguish between these types.

History and imaging findings may support one etiology of pleural effusion over another, but analysis of the pleural fluid provides more definitive diagnosis as well as therapeutic management in cases where the pleural effusion is impeding respiratory status.

Transudative pleural effusions are due to conditions in which there is an imbalance in hydrostatic and oncotic forces such as with heart failure, cirrhosis, or nephrotic syndrome.

Exudative effusions are due to inflammation from infection or noninfectious etiologies, injury, malignancy, and impaired lymphatic drainage. The primary method of distinguishing transudate from exudate is Light's criteria:
  • Pleural fluid protein to serum protein ratio >0.5, or
  • Pleural fluid lactate dehydrogenase (LDH) to serum LDH ratio >0.6, or
  • Pleural fluid LDH >2/3 upper limit of laboratories' normal LDH
Any of the above indicate exudate. pH should be checked on any fluid sampled from a thoracentesis as pH <7.2 indicates the need for drainage of the collection given the high risk for complicated parapneumonic effusion or empyema.


J90 – Pleural effusion, not elsewhere classified

60046008 – Pleural effusion

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

The differential is vast and often requires a careful history and, ultimately, correlation with thoracentesis and fluid sampling. The differential includes:

Best Tests

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Management Pearls

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Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

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Last Reviewed: 06/19/2018
Last Updated: 07/13/2018
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Pleural effusion
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Pleural effusion : Cough, Cyanosis, Pleuritic chest pain, Dyspnea, Dullness to percussion, Decreased breath sounds, RR increased
Imaging Studies image of Pleural effusion
67 year old female with metastatic non-small-cell lung adenocarcinoma who presented with recurrent pleural effusions requiring multiple therapeutic thoracenteses, and eventually a long-term tunneled catheter prior to hospice. Sequential axial non-contrast CT image of the chest viewed in soft-tissue windows through the lower chest. Sequential CT images obtained during placement of a left pleural drainage catheter show loculated fluid of near-water attenuation within the posterior, lateral, and anterior pleural spaces (straight black arrows), with resultant atelectatic/collapsed lung (straight white arrow). Note the thickened parietal pleura (straight red arrow), and the presence of fibrous bands (curved red arrow). A guidance needle approaches the left lateral inferior pleural space and is replaced by a pigtail catheter. Not unexpected is a small amount of air within the pleural space following placement. TPA was instilled via the catheter the following day in an attempt to disrupt the loculations.
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