• Clinical science
  • Physician

Pleural effusion


Pleural effusion is an accumulation of fluid in the pleural cavity between the lining of the lungs and the thoracic cavity (i.e., the visceral and parietal pleurae). The pleural fluid is called a transudate if it permeates (transudes) into the pleural cavity through the walls of intact pulmonary vessels. It is called an exudate if it escapes (exudes) into the pleural cavity through lesions in blood and lymph vessels, e.g., as caused by inflammation and tumors. The accumulation of transudate is typically due to increased hydrostatic pressure (e.g., in congestive heart failure) and/or decreased oncotic pressure (e.g., in cirrhosis or nephrotic syndrome). Since transudate is a filtrate, it is typically a clear fluid with a low protein and cell content. By contrast, the lesions responsible for the outflow of exudate allow larger molecules and even solid matter to pass into the pleural cavity. For this reason, exudate is a cloudy fluid with a high protein and cell content. The effusion follows gravity and, unless the patient is bedridden, collects in the lower margins of the pleural cavity. Percussion over the area of effusion generates a dull tone, and breath sounds are diminished or completely absent on auscultation. Chest x-ray and ultrasound are usually performed as first-line tests to diagnose pleural effusion, but chest CT is sometimes required (e.g., for very small effusions). Thoracentesis with pleural fluid analysis is required to establish the underlying diagnosis in most pleural effusions and can also serve a therapeutic role. Treatment should focus on correcting the underlying condition.


Transudative pleural effusion

Exudative pleural effusion
Common causes


Clinical features

Symptoms [5]

Physical exam findings

  • Inspection and palpation
  • Auscultation
  • Percussion: dullness over the area of effusion

Subtypes and variants

Parapneumonic effusion and pleural empyema [6][7][8][9]

Chylothorax [14]

Pseudochylothorax [15][14]

In contrast to chylothorax, a pseudochylothorax is characterized by high cholesterol and low triglyceride levels in the pleural fluid. The presence of cholesterol crystals may also help differentiate a pseudochylothorax from a chylothorax.

Hemothorax [16]

A hemothorax, however small, must always be drained because blood in the pleural cavity will clot if not evacuated, resulting in a trapped lung or an empyema.

Malignant pleural effusion [17]



Imaging can confirm a pleural effusion, but analysis of the pleural fluid (via thoracentesis) is usually required to establish the underlying etiology.


Chest x-ray

  • Very small pleural effusions (< 300 mL) may not be visible on a chest x-ray but can be detected on ultrasound.
  • Findings [19]
  • Lateral decubitus view: can help determine whether the fluid is encapsulated (loculated) or free [20][21]

Ultrasound [14][19]

Chest CT [14]

  • More sensitive than CXR and ultrasound in identifying small pleural effusions but not required for diagnosis
  • Measurement of fluid density on CT scan may provide a clue to the underlying etiology (e.g., hyperattenuation of blood in hemothorax).
  • Consider IV contrast if there is a concern for underlying malignancy (e.g., heavy asbestos exposure history).


  • Aspiration of fluid from the pleural space for diagnostic (e.g., transudate vs. exudate) and/or therapeutic purposes
  • Indications
    • Any new unilateral effusion > 1 cm on x-ray in an undiagnosed patient
    • History of malignant tumor with effusion > 1 cm on x-ray
    • Large effusion with dyspnea and/or cardiac decompensation
Pleural fluid analysis [22][23][24][14]
Transudative effusion Exudative effusion
Physical appearance
  • Does not froth or form clots
  • Cloudy or straw-colored fluid (may rarely be hemorrhagic)
  • Froths when shook and forms clots when left standing
Specific gravity
  • ≤ 1.016
  • > 1.016


Normal pH ∼ 7.6

  • 7.4–7.55
  • ≥ 60 mg/dL
  • < 60 mg/dL
  • ≥ 60 mg/dL
Total protein
  • ≤ 30 g/L
  • > 30 g/L
Light's criteria Pleural fluid protein:serum protein ratio
  • ≤ 0.5
  • > 0.5
Pleural fluid LDH:serum LDH ratio
  • ≤ 0.6
  • > 0.6
Pleural fluid LDH (lactate dehydrogenase)
  • < ⅔ the upper limit of normal serum LDH
  • Pleural fluid LDH > ⅔ the upper limit of normal serum LDH
  • Very high LDH levels (e.g., > 1000 IU/L) suggest empyema, malignancy, or rheumatoid effusion.

Transudate is usually clear, has a decreased cell count, and has low levels of protein, albumin, and LDH. Exudate typically appears cloudy, has an increased cell count, and has high levels of protein, albumin, and LDH.

Think MEAT to memorize causes of pulmonary effusion with decreased glucose content: M = Malignancy, E = Empyema, A = Arthritis (rheumatoid pleurisy), T = Tuberculosis!

Pleural fluid with a bloody appearance suggests a malignant etiology or hemothorax!



A chest x-ray should be performed after each of these procedures in order to rule out iatrogenic pneumothorax!

Acute management checklist

  • 1. Kasper DL, Fauci AS, Hauser SL, Longo DL, Lameson JL, Loscalzo J. Harrison's Principles of Internal Medicine. New York, NY: McGraw-Hill Education; 2015.
  • 2. Le T, Bhushan V, Chen V, King M. First Aid for the USMLE Step 2 CK. McGraw-Hill Education; 2015.
  • 3. Jenkins B, McInnis M, Lewis C. Step-Up to USMLE Step 2 CK. Lippincott Williams & Wilkins; 2015.
  • 4. McGrath EE, Blades Z, Anderson PB. Chylothorax: Aetiology, diagnosis and therapeutic options. Respir Med. 2010; 104(1): pp. 1–8. doi: 10.1016/j.rmed.2009.08.010.
  • 5. Saguil A, Wyrick K, Hallgren J. Diagnostic approach to pleural effusion. Am Fam Physician. 2014; 90(2): pp. 99–104. pmid: 25077579.
  • 6. Rubins J. Pleural Effusion. In: Pleural Effusion. New York, NY: WebMD. http://emedicine.medscape.com/article/299959-workup. Updated June 30, 2016. Accessed February 14, 2017.
  • 7. Ward MA. Empyema and Abscess. In: Empyema and Abscess. New York, NY: WebMD. http://emedicine.medscape.com/article/807499-clinical#showall. Updated March 18, 2015. Accessed February 13, 2017.
  • 8. Strange C. Parapneumonic effusion and empyema in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/parapneumonic-effusion-and-empyema-in-adults?source=search_result&search=pleural%20empyema&selectedTitle=1~150. Last updated December 20, 2016. Accessed February 13, 2017.
  • 9. Gaillard F. Empyema vs pulmonary abscess. https://radiopaedia.org/articles/empyema-vs-pulmonary-abscess-2. Accessed April 18, 2018.
  • 10. Kasper DL, Fauci AS, Hauser S, Longo D, Jameson LJ, Loscalzo J . Harrisons Principles of Internal Medicine . New York, NY: McGraw-Hill Medical Publishing Division; 2016.
  • 11. Tao Le, Vikas Bhushan, Deol M, Reyes G. First Aid for the USMLE Step 2 CK, Tenth Edition. New York: McGraw-Hill Education; 2018.
  • 12. King, Thompson. Radiological perspectives in empyema: Childhood respiratory infections. British Medical Bulletin. 2002; 61(1): pp. 203–214. doi: 10.1093/bmb/61.1.203.
  • 13. Weerakkody. Thoracic empyema. https://radiopaedia.org/articles/thoracic-empyema-1. Accessed May 13, 2019.
  • 14. Hooper et al. Investigation of a unilateral pleural effusion in adults: British Thoracic Society pleural disease guideline 2010. Thorax. ; 65: pp. ii4–ii17. doi: 10.1136/thx.2010.136978.
  • 15. Lama et al. Characteristics of patients with pseudochylothorax—a systematic review. Journal of Thoracic Disease. 2016; 8(8): pp. 2093–2101. doi: 10.21037/jtd.2016.07.84.
  • 16. Boersma et al. Treatment of haemothorax. Respiratory Medicine. 2010. doi: 10.1016/j.rmed.2010.08.006.
  • 17. Psallidas et al. Malignant pleural effusion: from bench to bedside. European Respiratory Review. 2016; 25(140): pp. 189–198. doi: 10.1183/16000617.0019-2016.
  • 18. Feller-Kopman et al. Management of Malignant Pleural Effusions. An Official ATS/STS/STR Clinical Practice Guideline. American Journal of Respiratory and Critical Care Medicine. 2018; 197(7). doi: 10.1164/rccm.201807-1415ST.
  • 19. Jones J, et al. Pleural effusion. https://radiopaedia.org/articles/pleural-effusion. Updated February 19, 2017. Accessed February 19, 2017.
  • 20. Northwestern Health Sciences University. Radiology of the Chest: Chapter Four: Diagnostic Radiographic Signs. url: http://www.nwhealth.edu/resource/radca/chest4.html Accessed February 19, 2017.
  • 21. Bien MY, Wu MP, Chen WL, Chung CL. VEGF correlates with inflammation and fibrosis in tuberculous pleural effusion. ScientificWorldJournal. 2015; 2015. doi: 10.1155/2015/417124.
  • 22. Heffner J; Broaddus V. Diagnostic evaluation of a pleural effusion in adults. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/diagnostic-evaluation-of-a-pleural-effusion-in-adults-initial-testing?search=pleural%20effusion&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1#H14. Last updated April 2, 2018. Accessed May 9, 2019.
  • 23. van Zuuren EJ, Trow T. Pleural Effusion. https://www.dynamed.com/topics/dmp~AN~T474331/Pleural-effusion. Updated August 24, 2017. Accessed November 26, 2017.
  • 24. Saguil A, Wyrick K, Hallgren J. Diagnostic approach to pleural effusion. Am Fam Physician. 2014; 90(2): pp. 99–104. url: http://www.aafp.org/afp/2014/0715/p99.html.
  • 25. Dweik RA. Pleural Disease. http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/pulmonary/pleural-disease/. Updated August 1, 2010. Accessed February 19, 2017.
  • 26. Le T, Bhushan V, Chen V, King M. First Aid for the USMLE Step 2 CK. New York, NY: McGraw-Hill Education; 2015.
  • 27. Heffner JE. Diagnostic Thoracentesis. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/diagnostic-thoracentesis. Last updated March 16, 2017. Accessed November 26, 2017.
  • Patrini D, Panagiotopoulos N, Pararajasingham J, Gvinianidze L, Iqbal Y, Lawrence DR. Etiology and management of spontaneous haemothorax. Journal of thoracic disease. 2015; 7(3): pp. 520–6. doi: 10.3978/j.issn.2072-1439.2014.12.50.
  • Inaba K, Lustenberger T, Recinos G, et al. Does size matter? A prospective analysis of 28–32 versus 36–40 French chest tube size in trauma. The Journal of Trauma and Acute Care Surgery. 2012; 72(2): pp. 422–427. doi: 10.1097/ta.0b013e3182452444.
  • Chalhoub M, Saqib A, Castellano M. Indwelling pleural catheters: complications and management strategies. Journal of Thoracic Disease. 2018; 10(7): pp. 4659–4666. doi: 10.21037/jtd.2018.04.160.
  • Kraus GJ. The Split Pleura Sign. Radiology. 2007; 243(1): pp. 297–298. doi: 10.1148/radiol.2431041658.
  • Hans H. Schild, Christian P. Strassburg, Armin Welz, Jörg Kalff. Treatment Options in Patients With Chylothorax. Deutsches Aerzteblatt Online. 2013; 110(48): pp. 819–826. doi: 10.3238/arztebl.2013.0819.
  • Rahman, NM, Chapman SJ, Davies RJO. Pleural effusion: a structured approach to care†. Br Med Bull. 2004; 72(1): pp. 31–47. doi: 10.1093/bmb/ldh040.
  • Lui MMS, Thomas R, Lee YCG. Complications of indwelling pleural catheter use and their management. BMJ Open Respiratory Research. 2016; 3(1): p. e000123. doi: 10.1136/bmjresp-2015-000123.
  • Cooke DT, David EA. Large-Bore and Small-Bore Chest Tubes. Thorac Surg Clin. 2013; 23(1): pp. 17–24. doi: 10.1016/j.thorsurg.2012.10.006.
  • Herold G. Internal Medicine. Cologne, Germany: Herold G; 2014.
  • Rahman NM, Maskell NA, Davies CWH, et al. The Relationship Between Chest Tube Size and Clinical Outcome in Pleural Infection. Chest. 2010; 137(3): pp. 536–543. doi: 10.1378/chest.09-1044.
  • Hallifax RJ, Psallidas I, Rahman NM. Chest Drain Size: the Debate Continues. Current Pulmonology Reports. 2017; 6(1): pp. 26–29. doi: 10.1007/s13665-017-0162-3.
  • Shen KR, Bribriesco A, Crabtree T, et al. The American Association for Thoracic Surgery consensus guidelines for the management of empyema. J Thorac Cardiovasc Surg. 2017; 153(6): pp. e129–e146. doi: 10.1016/j.jtcvs.2017.01.030.
  • Meeker JW, Jaeger AL, Tillis WP. An uncommon complication of a common clinical scenario: exploring reexpansion pulmonary edema with a case report and literature review. Journal of Community Hospital Internal Medicine Perspectives. 2016; 6(3): p. 32257. doi: 10.3402/jchimp.v6.32257.
  • Verhagen M, van Buijtenen JM, Geeraedts LMG. Reexpansion pulmonary edema after chest drainage for pneumothorax: A case report and literature overview. Respiratory Medicine Case Reports. 2015; 14: pp. 10–12. doi: 10.1016/j.rmcr.2014.10.002.
  • Kwon YS. Pleural Infection and Empyema. Tuberculosis and Respiratory Diseases. 2014; 76(4): p. 160. doi: 10.4046/trd.2014.76.4.160.
  • Socransky S, Wiss R, Hall G, Ho B, Skinner A, Turner J, Woo M, Chen R. Point-of-Care Ultrasound for Emergency Physicians. The EDE 2 Course Inc.; 2013.
  • Yashant Aswani, Priya Hira. Pancreaticopleural Fistula: A Review. JOP. Journal of the Pancreas. 2015; Vol 16: pp. No 1 (2015): January–p. 1. doi: 10.6092/1590-8577/2915.
  • Hallifax RJ, Talwar A, Wrightson JM, Edey A, Gleeson FV. State-of-the-art: Radiological investigation of pleural disease. Respir Med. 2017; 124: pp. 88–99. doi: 10.1016/j.rmed.2017.02.013.
  • Schweigert M, Solymosi N, Dubecz A, Ofner D, Stein HJ. Length of nonoperative treatment and risk of pleural empyema in the management of pancreatitis-induced pancreaticopleural fistula. Am Surg. 2013; 79(6): pp. 614–9. pmid: 23711272.
  • Porcel JM. Chest Tube Drainage of the Pleural Space: A Concise Review for Pulmonologists. Tuberculosis and Respiratory Diseases. 2018; 81(2): p. 106. doi: 10.4046/trd.2017.0107.
  • Machado NO. Pancreaticopleural Fistula: Revisited. Diagnostic and Therapeutic Endoscopy. 2012; 2012: pp. 1–5. doi: 10.1155/2012/815476.
  • Zarogoulidis K, Zarogoulidis P, Darwiche K, et al. Malignant pleural effusion and algorithm management. Journal of thoracic disease. 2013; 5 Suppl 4: pp. S413–9. doi: 10.3978/j.issn.2072-1439.2013.09.04.
  • Walls R, Hockberger R, Gausche-Hill M. Rosen's Emergency Medicine. Philadelphia, PA: Elsevier Health Sciences; 2018.
  • Mandell LA, Wunderink RG, Anzueto A, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults. Clinical Infectious Diseases. 2007; 44(Supplement_2): pp. S27–S72. doi: 10.1086/511159.
  • Karkhanis V, Joshi J. Pleural effusion: diagnosis, treatment, and management. Open Access Emergency Medicine. 2012: p. 31. doi: 10.2147/oaem.s29942.
  • Metlay JP, Waterer GW, Long AC, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. Am J Respir Crit Care Med. 2019; 200(7): pp. e45–e67. doi: 10.1164/rccm.201908-1581st.
  • Goldman L, Schafer AI. Goldman-Cecil Medicine, 2-Volume Set. Elsevier; 2019.
  • Roberts JR. Roberts and Hedges' Clinical Procedures in Emergency Medicine and Acute Care. Philadelphia, PA: Elsevier; 2018.
  • American College of Surgeons and the Committee on Trauma. ATLS Advanced Trauma Life Support. Chicago: American College of Surgeons; 2018.
  • Detterbeck FC, Lewis SZ, Diekemper R, Addrizzo-Harris D, Alberts WM. Diagnosis and Management of Lung Cancer, 3rd ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest. 2013; 143(5): pp. 7S–37S. doi: 10.1378/chest.12-2377.
  • Davies HE, Davies RJO, Davies CWH. Management of pleural infection in adults: British Thoracic Society pleural disease guideline 2010. Thorax. 2010; 65(Suppl 2): pp. ii41–ii53. doi: 10.1136/thx.2010.137000.
  • Simoff MJ, Lally B, Slade MG, et al. Symptom Management in Patients With Lung Cancer. Chest. 2013; 143(5): pp. e455S–e497S. doi: 10.1378/chest.12-2366.
  • Kasmani R, Irani F, Okoli K, Mahajan V. Re-expansion pulmonary edema following thoracentesis. Can Med Assoc J. 2010; 182(18): pp. 2000–2002. doi: 10.1503/cmaj.090672.
  • Chubb SP, Williams RA. Biochemical Analysis of Pleural Fluid and Ascites. The Clinical biochemist. Reviews. 2018; 39(2): pp. 39–50. pmid: 30473591.
  • Wilcox ME, Chong CAKY, Stanbrook MB, Tricco AC, Wong C, Straus SE. Does This Patient Have an Exudative Pleural Effusion?. JAMA. 2014; 311(23): p. 2422. doi: 10.1001/jama.2014.5552.
  • Puri V, Pyrdeck TL, Crabtree TD, et al. Treatment of Malignant Pleural Effusion: A Cost-Effectiveness Analysis. Ann Thorac Surg. 2012; 94(2): pp. 374–380. doi: 10.1016/j.athoracsur.2012.02.100.
  • Romero-Candeira S, Fernández C, Martı́n C, Sánchez-Paya J, Hernández L. Influence of diuretics on the concentration of proteins and other components of pleural transudates in patients with heart failure. Am J Med. 2001; 110(9): pp. 681–686. doi: 10.1016/s0002-9343(01)00726-4.
  • Cafarotti S, Dall’Armi V, Cusumano G, et al. Small-bore wire-guided chest drains: Safety, tolerability, and effectiveness in pneumothorax, malignant effusions, and pleural empyema. J Thorac Cardiovasc Surg. 2011; 141(3): pp. 683–687. doi: 10.1016/j.jtcvs.2010.08.044.
  • Sahn SA. Diagnosis and Management of Parapneumonic Effusions and Empyema. Clinical Infectious Diseases. 2007; 45(11): pp. 1480–1486. doi: 10.1086/522996.
  • Morgan CK, Bashoura L, Balachandran D, Faiz SA. Spontaneous Hemothorax. Annals of the American Thoracic Society. 2015; 12(10): pp. 1578–1582. doi: 10.1513/annalsats.201505-305cc.
last updated 04/08/2020
{{uncollapseSections(['uAaplM', 'wAahNM', 'xAaENM', 'NSc--b0', 'AAaRmM', '-AaDmM', '2_XTn00'])}}