Pearls and myths in pleural fluid analysis

Respirology. 2011 Jan;16(1):44-52. doi: 10.1111/j.1440-1843.2010.01794.x.


Virtually all patients with a newly discovered pleural effusion should undergo thoracentesis to aid in diagnosis and management. The routine pleural fluid (PF) evaluation usually includes the following: cell count and differential; tests for protein, LDH, glucose, adenosine deaminase, cytology and, if infection is a concern, pH and bacterial and mycobacterial cultures. Distinguishing transudates from exudates with Light's criteria is a pragmatic first step. If the effusion is an exudate, various PF tests have proven diagnostic utility: adenosine deaminase levels >35 IU/L usually indicate tuberculosis in lymphocyte-predominant PF; pH < 7.2 or glucose less than 60 mg/dL allow the clinician to identify complicated parapneumonic effusions; and conventional cytology may reveal malignant cells in 60% of the patients with malignant effusions. A number of optional PF tests may complement the diagnostic approach to an undiagnosed pleural effusion. For example, natriuretic peptide assays significantly improve the accuracy of a diagnosis of cardiac pleural effusion, whereas PF mesothelin levels greater than 20 nmol/L are highly suggestive of mesothelioma.

Publication types

  • Review

MeSH terms

  • Adenosine Deaminase / analysis
  • Exudates and Transudates* / chemistry
  • Exudates and Transudates* / cytology
  • Exudates and Transudates* / microbiology
  • Glucose / analysis
  • HIV Infections / complications
  • Humans
  • Leukocyte Count
  • Mesothelioma / diagnosis
  • Natriuretic Peptides / analysis
  • Neoplasm Metastasis
  • Paracentesis / methods
  • Pleural Effusion / diagnosis*
  • Pleural Effusion / microbiology
  • Pleural Effusion / pathology
  • Pleural Neoplasms / diagnosis
  • Pulmonary Embolism / complications
  • Pulmonary Embolism / diagnosis
  • Tuberculosis, Pulmonary / diagnosis


  • Natriuretic Peptides
  • Adenosine Deaminase
  • Glucose