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
1 | 2 | 3 |
---|---|---|
Pleural fluid | Test indicated | Interpretation |
Bloody | Haematocrit | Comparison to serum Haematocrit
|
Cloudy or turbid | Triglycerides | >110mg/dL-chylothorax |
Putrid odour | MCS | Possible 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
- Low
- 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)
- Repeated testing confirms continuation or 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 – Pleural effusion
- CCC – Pleural tap
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BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Associate Professor Curtin Medical School, Curtin University. Emergency physician, Sir Charles Gairdner Hospital. Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | Twitter |