Pleural Fluid Analysis

A pleural effusion is a collection of fluid in the pleural space. Pleural effusion are the result of :

  • Increased fluid accumulation
  • Decreased lymphatic clearance of fluid
    • Obstruction to drainage
    • Increased venous pressure
  • Pleural effusions are most commonly caused by CCF, Infection (pneumonia) and Malignancy
  • Pleural Fluid may be examined by a pleural tap or thoracocentesis

Common causes

  • Exudate (local disease) (High protein). Local factors influence the accumulation or clearance of fluid.
    • Malignancy – Lung, breast, pleural.
    • Infection – Pneumonia, empyema, pleuritis, viral disease
    • Autoimmune – Rheumatoid, SLE
    • Vascular – PTE
    • Cardiac – Pericarditis, CABG
    • Respiratory – Haemothorax, Chylothorax
    • Abdominal – Subphrenic abscess
  • Transudate (systemic illness) (Low protein <30g). Imbalance between oncotic and hydrostatic pressures
    • Cardiac – CCF, PTE
    • Liver – Ascites, Cirrhosis
    • Renal – Glomerulonephritis, Nephrotic syndrome
    • Ovarian – Meigs syndrome
    • Autoimmune – Sarcoid
    • Thyroid – Myxoedema

Differentiation of exudate and transudate fluid

  • Aims to identify local from systemic illness. Common causes can then be actively sought and treated
  • Use Light’s criteria is moderately sensitive for differentiation, further tests are then required to further define the exudate

Pleural fluid from thoracocentesis

123
Pleural fluidTest indicatedInterpretation
BloodyHaematocrit

Comparison to serum Haematocrit

  • <1% - non-significant
  • 1-20% - Cancer, PTE, trauma, pneumonia
  • >50% - Haemothorax
Cloudy or turbidTriglycerides>110mg/dL-chylothorax
Putrid odourMCSPossible anaerobic infection

Pleural fluid laboratory findings

  • Lights criteria (High protein and LDH = exudate), determines presence of exudate with protein and LDH levels
    • Pleural fluid protein to serum protein ratio >0.5
    • Pleural fluid LDH to serum LDH ratio >0.6
    • Pleural fluid level >2/3 of upper value for serum LDH
  • Additional criteria – Confirm exudate if results equivocal
    • Serum albumin – pleural fluid albumin <1.2g/dL

Further tests

If exudate is confirmed, further testing required to evaluate cause of exudate

  • Differential cell count (predominance of white cells)
    • Neutrophils – PTE, pancreatitis, pneumonia, empyema
    • Lymphocytes – Cancer, TB pleuritis
    • Eosinophila – Pneumothorax, haemothorax, asbestosis, Churg-Strauss
    • Mononuclear cells – Chronic inflammatory process
  • Gram stain and culture and cytology
    • Use blood culture bottles and specimen jars – especially if chronic illness or suspect TB or fungus
    • Cytology useful in cases of suspected malignancy
  • Glucose
    • Low
      • Common: Infection (pneumonia) and malignancy
      • Rare: TB, haemothorax, Churg-Strauss
  • LDH level – This is classically high in exudates
    • Repeated testing confirms continuation or cessation of process
      • Increasing LDH (ongoing inflammation)
      • Decreasing LDH (cessation of process)
  • Pleural fluid pH (Low glucose and pH = infection or malignancy)
    • Taken if suspect pneumonic or malignant process (Low glucose)
    • <7.20 with pneumonia…Drain the fluid
    • <7.20 with malignancy …Life expectancy 30 days
  • Amylase
    • Useful if suspect pancreatitis as cause

References and Links


CCC 700 6

Critical Care

Compendium

Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM with a passion for rugby; medical history; medical education; and informatics. Asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | vocortex |

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