Pleural Effusions and Light’s Criteria

Dr. Vadia discussed the topic of pleural effusions during afternoon report today. Below is an outline to the diagnostic and therapeutic approaches to pleural effusion management.

Who needs a thoracentesis?: Any new pleural effusion should be tapped, UNLESS:

1. There is not enough fluid to tap
2. The patient has CHF, bilateral effusions, is afebrile and the effusion resolves within 3 days.

Step 1: Is the effusion exudative? 

  • Ddx for Transudative Effusion includes: CHF (90%), cirrhosis (hepatic hydrothorax), pulmonary embolism, nephrotic syndrome, peritoneal dialysis, myxedema, constrictive pericarditis, SVC syndrome.
  • Ddx for Exudative Effusion includes: Infection, cancer, connective tissue disease, pancreatitis, uremia, chylothorax, drug reaction, post-MI/CABG, esophageal rupture.
  • Check serum and fluid LDH and total using Light’s criteria (Satisfying any ONE criterium means it is exudative):
    • Pleural Total Protein/ Serum Total Protein > 0.5
    • Pleural LDH/ Serum LDH > 0.6
    • Pleural LDH > 2/3s of the upper limit of normal for serum LDH
    • **For patient with high suspicion for transudate, but meets Light’s Criteria (ie CHF patient recently diuresed), Dr. Light recommends a serum albumin – pleural albumin < 1.2 mg/dl, to confirm the effusion is exudative.

Step 2: If exudative, obtain the following pleural fluid tests:

  • Cell Count with differential:
    • PMNs > 50%: Parapneumonic, PE, pancreatitis.
    • Lymphs >50%: Cancer, TB, fungus or post-surgery
    • Eos >10%: PTX, hemothorax, drug reaction, asbestos, parasite infection, Churg-Strauss
  • Culture and Smear/Gram Stain: Yield is increased if fluid sent in blood culture bottles. Send for fungus and mycobacteria if pleural lymphs > 50 % or clinical picture is suspicious. Yield in Tb is <50%. 
  • Glucose: Level <60 mg/dL is seen in complicated parapneumonic effusion, malignancy, hemothorax, Tb, RA, SLE, Churg-Strauss, parasite infection.
  • Cytology: A case series of 971 lung cancer patients reported 7% prevalence of pleural effusion on chest xray and 40% of these pleural effusions had positive cytology. If cytology is negative and cancer is suspected, pleural biopsy should be performed.
  • Consider Adenosine Deaminase(ADA) for Tb: At least 50% of tuberculous pleural effusions do not involve other organs and are therefore difficult to diagnose. ADA levels >40-60 U/L in the setting of a lymphocytic effusion are specific for Tb.
  • Consider Amylase: Elevated in patients with pancreatitis, esophageal rupture, and malignancies.

Step 3: What if the diagnosis is unclear from these tests?

The cause of 15% of exudative effusions is not determined. For both transudative and exudative effusions without a cause, pulmonary embolism should be considered. Further evaluation by pleural biopsy via thoracoscopy or open biopsy is indicated for undiagnosed, unresolved exudative effusion.