Linking To And Excerpting From CoreIM’s “Pleural Effusions: 5 Pearls Segment”

Posted on July 11, 2025 by Tom Wade MD

Today, I review, link to, and excerpt from CoreIM‘s Pleural Effusions: 5 Pearls Segment.

All that follows is from the above resource.

Pleural Effusions: 5 Pearls Segment

Posted: July 9, 2025
By: Dr. Kalaila Pais, Dr. Christopher Kapp, Dr. David Furfaro, Dr. Kristina Montemayor and Dr. Shreya P. Trivedi
Graphic: Dr. Jesse Powell
Peer Review: Dr. Kanupriya Soni, Dr. Laura McNamara, Dr. Michael Ferrera, Dr. Mihir Parikh

Podcast: Play in new window | Download

Time Stamps

  • Interpretation of Pleural Fluid Studies and Common Pleural Diseases
  • Imaging Pearls and Thoracentesis Indications
  • Deciding on Thoracentesis
  • Light’s Criteria and Pseudo Exudates
  • Pleural Fluid Studies: pH and Cell Differential
  • Diagnosing and Treating Parapneumonic Effusions
  • Malignant Pleural Effusions: Diagnosis and Management
Sponsor: Oakstone CME’s ACP MKSAP Audio Companion
Use the code “CORE25” for 25% off: https://www.coreimpodcast.com/MKSAP

Show Notes

  • Pearl 1: Review of Pleural Effusions
    • Types of pleural effusions
      • Pleural effusions are a pathologic state in which more fluid accumulates between the visceral and parietal pleura than is physiologic.
      • Transudative pleural effusions occur due to increased hydrostatic and decreased oncotic pressure
      • Exudative effusions occur due to a process causing increased capillary permeability allowing complex materials entering the pleural space
    • Points to consider when discussing diagnostic thoracentesis
      • Laterality of the effusion: while bilateral effusions tend to be due to transudative processes, a new unilateral thoracentesis warrants diagnostic tap
      • Chronicity of the effusion: consider diagnostic thoracentesis for new unilateral pleural effusions or treatment refractory bilateral pleural effusions
        • Patient risk factors: consider diagnostic thoracentesis in patients with underlying malignancy, concern for infection, recent thoracic surgery
    • Do not anchor, up to 30% of pleural effusions have more than one etiology
    • Ultrasounding pleural effusions
      •  Sensitive test which is easiest to do repeatedly at the bedside and can provide features of the effusion
  • Pearl 2: Light’s Criteria and Pseudoexudates
    • Light’s criteria 
      • Pleural fluid-to-serum protein ratio greater than 0.5
      • Pleural fluid-to-serum LDH ratio greater than 0.6
      • Pleural fluid LDH greater than 0.67 (ie, two-thirds) the upper limits of the laboratory’s normal serum LDH
    • Benefits to Light’s criteria is its simplicity and high sensitivity for exudative effusions. However, some caveats is that it duplicates its use of LDH and it can be inaccurate in patients on chronic diuretic therapy – pseudoexudates
    • Pseudoexudates
      • Effusions where the underlying etiology is transudative but is classified as exudative based on Light’s criteria. Some additional tests that may clue us that the effusion is transudative is:
    • Pleural fluid only three test confirmation
      • Classified pleural effusions using pleural protein, cholesterol and LDH without the use of serum tests.
        • protein >  3.0 g/dL
        • cholesterol >  45-55 mg/dL
        • LDH > 0.45-0.67 times the lab ULN.
      • May be useful in scenarios when the Light’s criteria is borderline positive or there is diagnostic uncertainty
  • Pearl 3: Interpreting Pleural Fluid Studies
    • pH
      • Levels:
        • Normal pH ~ 7.60
        • Transudative effusions: pH 7.40-7.55
        • Exudative effusions: pH < 7.30;
      • Considerations of interpreting pH
        • Pleural fluid for pH testing should be collected anaerobically in a heparinized syringe and measured in a blood-gas machine.
        • Artificial elevation of pH can be due to air contamination in the sample.
        • Artificial reduction can be due to contamination with heparin or lidocaine.
        • If the fluid is really chronic and has been there for a long time and it’s cellular, the pH can be low even if without some active very infected process. ***
    • Cell count and differential 
      • Elevated neutrophils (>50%) are seen in acute processes like parapneumonic effusions, empyema, PE
      • Lymphocytic predominance (>50%) is seen in TB, longstanding pleural effusions, CHF or malignancy.
        • Pleural fluid lymphocytosis > 90 percent suggests tuberculosis or lymphoma.
      • Pleural eosinophilia (>10%) could be due to a variety of causes: malignancy, infection, trauma, drugs, toxin, inflammation. It can signify recent air or blood in pleural space.
        • No diagnosis is ever obtained in as many as one third of patients with eosinophilic pleural effusion
      • Red blood cells: Ratio of pleural fluid to blood Hct > 0.5 is diagnostic of hemothorax
    • Gram stain and cultures
      • Positive Gram stain and cultures are generally diagnostic of a parapneumonic effusion, and frank pus is diagnostic of empyema.
      • Pleural fluid should be placed in blood culture bottles and a sterile container, because a small but well-conducted series showed a 20% absolute increase in microbiologic yield with this strategy
    • Adenosine deaminase
      • The most common diagnostic threshold used to establish a TB pleural effusion is a pleural fluid adenosine deaminase (ADA) level greater than 40 U/L.
      • ADA can also be elevated in hematologic malignancies like lymphoma, brucellosis, Q fever and rheumatoid arthritis
    • Glucose
      • Glucose concentration in pleural fluid should be the same as that of the blood. If glucose is low in pleural fluid, consider empyema, TB, malignancy or RA to name a few
    • pro-BNP
      • There is a high correlation between serum and pleural pro-BNP and so unless multiple etiologies are suspected, pleural pro-BNP may add little diagnostic value ***
      • If there is diagnostic uncertainty that the pleural effusion is of cardiac origin, pleural fluid NT-pro-BNP is a useful biomarker with high diagnostic accuracy.***
    • Triglycerides
      • A level  > 110 mg/dl supports a chylothorax but a level < 50 rules it out
    • Amylase
      • When it is greater than the upper limit of normal, it suggests malignancy (<20 percent), pancreatic disease, esophageal rupture
  • Pearl 4: Parapneumonic Effusions
    • Nearly 50% of bacterial pneumonias have associated pleural effusions, but most do not result in complicated effusions or empyemas.
    • Spectrum of parapneumonic effusions
      • Uncomplicated parapneumonic effusions: exudative,  neutrophilic effusion, Gram stain and culture are negative, glucose level > 60 mg/dl, pH > 7.20.
      • Complicated parapneumonic effusions: glucose level < 60mg/dl, pH < 7.20, gram stain and culture may or may not be negative depending on the stage of disease, and loculations/septations may be seen on US.
      • Empyema: collection of bacteria or pus in the pleural space
    • Management of parapneumonic effusions
      • Antibiotics: Treatment of parapneumonic effusion includes appropriate antibiotic therapy (including anaerobic coverage) together with drainage of pleural fluid as indicated.
      • Chest tube placement: Pigtail chest tube is as good as large bore surgical chest tube
      • Enzymatic Treatment and MIST trials:
        • MIST 1: The intrapleural administration of streptokinase does not improve mortality, the rate of surgery, or the length of the hospital stay among patients with pleural infection.
        • MIST 2: Intrapleural t-PA–DNase therapy improved fluid drainage in patients with pleural infection and reduced the frequency of surgical referral and the duration of the hospital stay. Treatment with DNase alone or t-PA alone was ineffective.
  • Pearl 5: Malignant Pleural Effusions
    • Suspicion of malignant pleural effusion (MPE) should be followed with drainage.
    • The yield for cytology is around 60%. The majority of MPEs will be detected within two attempts at sampling, so if the first tap is negative, do another.
    • If a diagnosis cannot be made with pleural fluid alone, a pleural biopsy is needed either via medical thoracoscopy from IP or VATS with thoracic surgery.
    • Management of recurrent MPEs
      • Repeated thoracentesis
        • Pros: Low risk procedure
        • Cons: Repeated thoracentesis requires repeated visits to the hospital.
        • It is reasonable to first trial pleural aspiration to assess symptomatic response prior to insertion of indwelling pleural catheters
      • Indwelling pleural catheter placement
        • If lungs are non-expandable and require intervention for symptomatic MPE, consider use of an indwelling pleural catheter rather than talc pleurodesis.
        • Pros:
          • simple to place
          • does not require repeated clinic/hospital visits,
        • Cons:
          • Psychological implications of having a semi-permanent tube drain inserted
          • Requires training for management
          • Higher risk for infection
      • Pleurodesis
        • In MPE patients with expandable lungs, talc slurry pleurodesis may improve quality of life, chest pain, breathlessness and pleurodesis rates.
        • Pros: Effective procedure
        • Cons: Invasive and painful procedure

 

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