Pleural Fluid Analysis (Diagnostic Tests)

Thoracentesis

• Indications: effusion without a secure clinical diagnosis (e.g., CHF) or small quantity
• Contraindications: none absolute, relative risk > benefit, bleeding diathesis, small effusion, mechanical ventilation, anticoagulation
• Complications:
  • Subjective: anxiety, site pain
  • Objective: pneumothorax (12% at a University H), 1/3-1/2 of those require check tubes; fluid contaminated with blood, "dry tap"; empyema; puncture of other organs (e.g., liver); hypoxemia and unilateral pulmonary edema only with therapeutic taps - usually large and occur with carcinoma or trapped lung
• Benefit: relief of dyspnea with therapeutic tape - via reduction of chest wall size even though hypoxemia occurs
• Diagnostic yield:
  • Almost 75% of thoracentesis yield a specific or presumptive diagnosis; 15-20% more are useful in management (e.g., rule out empyema)
  • Specific diagnoses: malignancy (cells), empyema (pus), tuberculosis pleurisy (AFB), fungal infection (KOH), lupus pleuritis (LE cells), chylothorax, urinothorax fluid creatinine/serum creatinine greater than 1), esophageal rupture (high fluid amylase, Ph about 6.0)
  • Tests that should be run (35-50 ml fluid): LDH, protein, WBC count and differential, glucose, Ph; concomitant serum protein, LDH, glucose; arterial pH if fluid pH <7.30 and acidemia is suspected. Supplement with other reasonably requested analyses cytology, cultures, smears, immunology, amylase, lipids, CEA, etc.
• Results:
  • Exudate vs. transudate:
    (1) Fluid/serum protein ratio > 0.5
    (2) Fluid/serum LDH ration > 0.6
    (3) Fluid LDH > 2/3 upper normal serum LDH; exudates have 1 or more; transudates none these characteristics
  • If LDH only is abnormal - consider malignancy or parapneumonic effusion
  • Protein may confuse: e.g., CHF <3 g/dl, but might be 3-4 g/dl if patient uses diuretics, or is chronic or recurrent
  • WBC: rarely diagnostic alone; > 50,000 in parapneumonic effusion, usually empyema; > 10,000 very inflammatory
    (1) Early, acute, PMN predominant
    (2) Later mononuclear - high counts suggest TB, carcinoma, lymphoma, sarcoidosis
    (3) Eosinophilia - 10% suggest benign, self- limited; commonly with air or blood in pleural space; consider: hemothorax, pulmonary infarction, pneumothorax, previous thoracentesis, parasitic diseases, fungi, drugs, asbestos; rare with TB or malignancy. In 1/3 "idiopathic"
    (4) Basophilia - 10%, rare; suggest leukemia
  • Mesothelial cells - paucity of cells occurs with chronic diffuse pleural lesions, e.g., TB, malignancy, empyema rheumatoid effusion, pleurodesis. If > 5%, essentially rules out TB
  • Bloody (> 100,000 cells/mm3): malignancy, trauma, pulmonary embolism, post-cardiac injury, asbestos pleurisy
  • Cytology: yields nearly 90% with malignancy as cause

Percutaneous Pleural Biopsy

• Indication: undiagnosed exudate, especially lymphocytic (yield: TB - 75%, over 90% with AFB culture of tissue; malignant 60%)
• Contraindications: obliterated pleural space, anticoagulation, uncooperative patient, bleeding diathesis
• Complications: similar to thoracentesis

Thoracoscopy

• Indications: controversial because it usually requires hospitalization, and only increased yield a small amount. Pleurodesis can be done at the same time
• Contraindications: like closed biopsy
• Complications: tumor seeding common

Open Biopsy

• With thoracotomy and autopsy, the "gold" standard - but risk and cost are relatively high