Physiology
Pleural Space Cell Content
- Pleural space normally contains 75% macrophages + 23% lymphocytes
Etiologies of Various Pleural Space Pressure States
CXR Findings
- Typical CXR Finding = Pleural Effusion with Contralateral Shift of Mediastinum
- CXR Finding in Presence of Trapped Lung, Fixed Mediastinum, or Co-Existent Atelectasis = Pleural Effusion with Ipsilateral Shift of Mediastinum (or Midline Mediastinum)
Pleural Fluid Criteria
General Comments
- LDH Ratio and Total Protein Ratio are Necessary from Light’s Criteria
- The pleural LDH <66% criterion does not add more in discriminative value
- Cut-Off Values for LDH and Total Protein Ratios: since there is not a discrete cut-off between values of LDH and total protein, the specified cut-off values give high sensitivity but lower specificity (ie: you will detect all true exudates, but you may misclassify some transudates as exudates, as in diuresed congestive heart failure cases)
Transudate (see Pleural Effusion-Transudate, [[Pleural Effusion-Transudate]])
- LDH Ratio <0.6
- Total Protein Ratio <0.5
- Pleural LDH <66% of Upper Limit of Normal Range for Serum LDH
- Pleural Cholesterol <55-60 mg/L
- Pleural/Serum Cholesterol Ratio: normal
- Serum-Pleural Albumin Gradient (SPAG) >1.2 g/dL
- If fluid clinically appears to be a transudate and SPAG >1.2, but Light’s criteria suggest exudate, fluid can be assumed to be a transudate (albumin is lower MW than other proteins and crosses capillary walls more easily)
Exudate (see Pleural Effusion-Exudate, [[Pleural Effusion-Exudate]])
- General Comments: pleural effusion is considered exudative if it meets any one of the following criteria, although LDH ratio and total protein ratio are the best criteria
- LDH Ratio >0.6
- Total Protein Ratio >0.5
- Pleural LDH >66% of Upper Limit of Normal Range for Serum LDH
- Pleural Cholesterol >55-60 mg/dL
- Pleural/Serum Cholesterol Ratio: elevated
- Serum-Pleural Albumin Gradient (SPAG) <1.2 g/dl
- If fluid clinically appears to be a transudate and SPAG >1.2, but Light’s criteria suggest exudate, fluid can be assumed to be a transudate (albumin is lower molecular weight than other proteins and crosses capillary walls more easily)
Bloody Effusion (see [[Pleural Effusion-Bloody Effusion]])
- RBC Count >100k
Hemothorax (see [[Pleural Effusion-Hemothorax]])
- Pleural Hct >50% of Serum Hct
Chylothorax (see [[Pleural Effusion-Chylothorax]])
- Pleural Fluid Triglyceride: elevated
- Trig >100 mg/dL: diagnoses chylothorax (chylothorax fluid clears with addition of ethyl ether)
- Trig <50 mg/dL: rules out chylothorax
- Trig 50-110 mg/dL: perform lipoprotein analysis for chylomicrons to diagnose chylothorax
- Pleural Fluid Chylomicron: seen
Pseudochylothorax (Cholesterol Pleurisy) (see [[Pleural Effusion-Pseudochylothorax]])
- Elevated cholesterol (>200 mg/dL), but no triglycerides or chylomicrons
Empyema (see [[Pleural Effusion-Parapneumonic]])
- Pus in the pleural space (with or without a positive gram stain)
Pleural Fluid pH
- Routine measurement of pleural pH is recommended only in patients with parapneumonic effusions
- Technique: collect blood aerobically in heparinized syringe (similar to ABG collection technique)
- Sample left open to air (or with sir bubble in the syringe) can have increase in pH due to loss of CO2 into the air
- In general, pleural fluid pH correlates with pleural fluid glucose
[Potts DE, Willcox MA, Good JTJ, et al: The acidosis of low-glucose pleural effusions. Am Rev Respir Dis 1978; 117:665-671]
Pleural Fluid Cholesterol
- Cholesterol is always very high (>200 mg/dL) in Pseudochylothorax (see [[Pleural Effusion-Pseudochylothorax]])
Pleural Fluid Triglycerides
- Trig >100 mg/dL: diagnoses chylothorax (chylothorax fluid clears with addition of ethyl ether)
- Trig <50 mg/dL: rules out chylothorax
- Trig 50-110 mg/dL: perform lipoprotein analysis for chylomicrons to diagnose chylothorax
Pleural Fluid Amylase
- Increased Pleural Fluid Amylase
- Esophageal Perforation (see Esophageal Perforation, [[Esophageal Perforation]])
- Amylase originates from salivary source
- Typically increased in pleural fluid within 2 hrs of perforation
- Pancreatico-Pleural Fistula: pleural fluid amylase is typically very high (>4000 IU/mL)
- Malignancy
- Approximately 10% of malignant effusions (due to non-pancreatic malignancy) have mildly elevated pleural amylase
- Pleural amylase in these cases is of the salivary isoenzyme type
- Esophageal Perforation (see Esophageal Perforation, [[Esophageal Perforation]])
Pleural Fluid Adenosine Deaminase (ADA)
- ADA is released from activated lymphocytes
- ADA is >45 U/mL in almost all patients with TB pleuritis
- However, elevated ADA can also seen in empyema, lymphoma, leukemia, and RA
- ADA may be less useful in Asians
- ADA is a sensitive marker for TB pleuritis even in the setting of HIV
[Baba K, Hoosen AA, Langeland N, et al: Adenosine deaminase activity is a sensitive marker for the diagnosis of tuberculous pleuritis in patients with very low CD4 counts. PLoS One 2008; 3:e2788]
Pleural Fluid ANA
- Pleural Fluid ANA: positive at >1:40 titer
- High Negative Predictive Value for Diagnosis of Lupus Pleuritis: positive pleural ANA is present in all cases of lupus pleuritis -> negative pleural ANA suggest that lupus pleuritis is not the etiology of the effusion
- Low Specificity for Diagnosis of Lupus Pleuritis: positive pleural ANA can also be seen in 11-27% of other effusions -> importantly, neither the titer of ANA, ratio between pleural and serum ANA, nor pattern of staining increase the specificity of the pleural ANA test for lupus pleuritis
- Pleural/serum ANA ratio is >1 (with pleural ANA >1:160) in SLE
Pleural Fluid RF
- Pleural titer >1:320 is seen in RA (this is usually higher than the concomitant serum titer)
Pleural Fluid Complement
- Decreased Pleural Fluid Complement
- Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis, [[Rheumatoid Arthritis]])
- Systemic Lupus Erythematosus (SLE) (see Systemic Lupus Erythematosus, [[Systemic Lupus Erythematosus]])
Pleural Fluid Immunocytometry
- Positive in Lymphoma-Associated Exudates (see Lymphoma, [[Lymphoma]])
Pleural Fluid Mesothelial Cells
- Decreased Pleural Fluid Mesothelial Cells
- Rheumatoid Arthritis (RA) (see Rheumatoid Arthritis, [[Rheumatoid Arthritis]])
- Tuberculosis (see Tuberculosis, [[Tuberculosis]])
- Increased Pleural Fluid Mesothelial Cells
- Radiation Pleuritis (see Radiation Pleuritis, [[Radiation Pleuritis]])
Pleural Fluid Interferon Gamma
- Elevated in TB pleuritis
Pleural Fluid TB PCR
- May be useful in diagnosis of TB pleuritis
- However, these tests have low sensitivity, often comparable to that of cultures alone
References
- Baba K, Hoosen AA, Langeland N, et al: Adenosine deaminase activity is a sensitive marker for the diagnosis of tuberculous pleuritis in patients with very low CD4 counts. PLoS One 2008; 3:e2788