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Pleural Effusion: Diagnostic Approach in Adults

Joy Shen-Wagner, MD
Christine Gamble, MD
Phyllis MacGilvray, MD

American Family Physician. 2023;108(5):464-475.

Author disclosure: No relevant financial relationships.

Pleural effusion affects 1.5 million patients in the United States each year. New effusions require expedited investigation because treatments range from common medical therapies to invasive surgical procedures. The leading causes of pleural effusion in adults are heart failure, infection, malignancy, and pulmonary embolism. The patient's history and physical examination should guide evaluation. Small bilateral effusions in patients with decompensated heart failure, cirrhosis, or kidney failure are likely transudative and do not require diagnostic thoracentesis. In contrast, pleural effusion in the setting of pneumonia (parapneumonic effusion) may require additional testing. Multiple guidelines recommend early use of point-of-care ultrasound in addition to chest radiography to evaluate the pleural space. Chest radiography is helpful in determining laterality and detecting moderate to large pleural effusions, whereas ultrasonography can detect small effusions and features that could indicate complicated effusion (i.e., infection of the pleural space) and malignancy. Point-of-care ultrasound should also guide thoracentesis because it reduces complications. Computed tomography of the chest can exclude other causes of dyspnea and suggest complicated parapneumonic or malignant effusion. When diagnostic thoracentesis is indicated, Light's criteria can help differentiate exudates from transudates. Pleural aspirate should routinely be evaluated using Gram stain, cell count with differential, culture, cytology, protein, l-lactate dehydrogenase, and pH levels. Additional assessments should be individualized, such as tuberculosis testing in high-prevalence regions. Parapneumonic effusions are the most common cause of exudates. A pH level less than 7.2 is indicative of complicated parapneumonic effusion and warrants prompt consultation for catheter or chest tube drainage, possible tissue plasminogen activator/deoxyribonuclease therapy, or thoracoscopy. Malignant effusions are another common cause of exudative effusions, with recurrent effusions having a poor prognosis.

Pleural effusion is excess fluid accumulation in the pleural space caused by disease or physiologic dysregulation and requires careful investigation to identify the underlying cause. A normal amount of pleural fluid (5 to 10 mL) is physiologic and allows for apposition and sliding of the visceral and parietal pleura and normal lung expansion. Pleural effusion results when fluid production exceeds absorption. Leading causes of pleural effusion in adults are heart failure, infection, malignancy, and pulmonary embolism.1,2 Transudative effusions are caused by disruptions in hydrostatic or oncotic pressures in heart failure, cirrhosis, or advanced kidney disease. Cirrhosis and portal hypertension may also cause ascitic fluid translocation across the diaphragm into the right hemithorax (hepatic hydrothorax). Inflammation of the pleural surface from pneumonia (parapneumonic effusion), malignancy, pulmonary embolism, medications,3 or autoimmune disease results in exudative fluid accumulation (Table 13–7 ).

SORT: KEY RECOMMENDATIONS FOR PRACTICE

Clinical recommendation Evidence rating Comments
If available, point-of-care ultrasound with chest radiography should be used in the initial evaluation of the pleural space to determine the size and character of the effusion.2,5,8,17,18 C Expert opinion and consensus guideline with disease-oriented evidence
If malignancy is suspected, further evaluation with computed tomography is indicated. However, a negative computed tomography result does not exclude malignancy.17 C Expert opinion, consensus guidelines
Diagnostic thoracentesis is typically indicated for pleural effusions that are new onset, unilateral, and larger than minimal, in the absence of clinically evident heart failure, cirrhosis, or kidney failure appropriately responsive to therapy. Therapeutic thoracentesis should be performed to relieve symptoms.2,5,17,18 C Expert opinion, consensus guidelines, and usual practice
Routine chest radiography after pleural aspiration is not required unless the patient is symptomatic, air is aspirated, or after multiple thoracentesis attempts.2,28,31,34 B Expert consensus based on multiple medium-size prospective cohort studies; systematic review
Ultrasound-guided thoracentesis should be used because it decreases complications from pneumothorax and solid organ puncture.5,11,17,18,26,28,33,35 B Expert consensus and guideline based on multiple small observational studies

A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to https://www.aafp.org/afpsort.

JOY SHEN-WAGNER, MD, FAAFP, is an associate professor in the Department of Family Medicine at the University of South Carolina School of Medicine Greenville and faculty and associate director of medical student education at the Prisma Health Family Medicine Residency Program, Greenville.

CHRISTINE GAMBLE, MD, is an assistant professor at the University of South Carolina School of Medicine Greenville; faculty at the Prisma Health Family Medicine Residency Program; and medical director at the Prisma Health Center for Family Medicine, Greenville.

PHYLLIS MACGILVRAY, MD, FAAFP, is a professor and senior associate dean for academic affairs at the University of South Carolina School of Medicine Greenville and faculty at the Prisma Health Family Medicine Residency Program.

Address correspondence to Joy Shen-Wagner, MD, FAAFP, 877 W Faris Rd., Greenville, SC 29605 (joy.shen-wagner@prismahealth.org). Reprints are not available from the authors.

Author disclosure: No relevant financial relationships.

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