A 65-year-old female, with a known medical history of rheumatoid arthritis, and a left mastectomy for breast cancer treated with radiotherapy 7 years ago, presents with respiratory failure requiring intubation and mechanical ventilation. Chest X-ray reveals a large left-sided pleural effusion, into which an intercostal catheter is placed.
With regard to this patient, discuss how examination of the pleural fluid may assist in identifying the cause of this effusion.
Appearance (1.5 marks)
Clear, straw-coloured – more likely transudate (although still may be exudate) Blood-stained – malignancy, pulmonary infarction
Yellow/green – rheumatoid Pus – empyema
Turbid – inflammatory exudate
Transudate vs exudate (3 marks)
Clearly some overlap, but in general terms Transudate – cardiac failure,
Exudate – malignancy, empyema, parapneumonic, , connective tissue disease (e.g. rheumatoid), pulmonary infarction, TB
Based on biochemical analysis
Different diagnostic criteria for distinguishing e.g. Light’s Criteria Rule
Exudate if at least one of the following; Pleural fluid protein / serum protein ratio > 0.5
Pleural fluid LDH / serum protein LDH ratio > 0.6
Pleural fluid LDH > 2/3 of the upper limit of the lab’s normal serum LDH
Pleural fluid pH < 7.30 - exudate, with following differentials more likely; Malignant effusion
Complicated parapneumonic effusion or empyema Rheumatoid pleural disease
pH < 7.2 is predictive of empyema, and is the best marker of a complicated parapneumonic effusion
Glucose – low concentration (< 3.3 mmol/L) or pleural fluid / serum glucose ratio < 0.5 not only supports exudate, but makes following differentials more likely;
Complicated parapneumonic effusion or empyema
Rheumatoid pleural disease (glucose can be particularly low) (1.5 marks)
Microscopy (1.5 marks)
Nucleated cell counts rarely diagnostic but may be supportive (e.g. >50,000/ml usually only complicated parapneumonic effusion/empyema)
Lymphocytosis – very high lymphocyte ratio (85-95% of total nucleated cells) suggests rheumatoid, TB,
Cytology (0.5 marks)
Malignant cells – overall sensitivity of only 60% in malignant effusions. Varies with type of malignancy.
Culture/Sensitivity (0.5 marks)
To achieve high marks candidates needed to demonstrate an understanding of how individual results point to specific diagnoses, rather than simply listing test options.
This question was not answered well. Those who provided a good diagnostic approach to the evaluation of pleural effusion in the clinical context scored higher compared to those who provided only a list of differential diagnoses. Many candidates did not know Light's criteria differentiating exudate from transudate.
Biochemistry and cytology are the main things one can order.
Cytology from the cell count:
Light, Richard W., et al. "Pleural effusions: the diagnostic separation of transudates and exudates." Annals of Internal Medicine 77.4 (1972): 507-513.
Light, Richard W. "Pleural effusion." New England Journal of Medicine 346.25 (2002): 1971-1977.
Shinto, Richard A., and Richard W. Light. "Effects of diuresis on the characteristics of pleural fluid in patients with congestive heart failure." The American journal of medicine 88.3 (1990): 230-234.
Light, Richard W., Yener S. Erozan, and Wilmot C. Ball. "Cells in pleural fluid: their value in differential diagnosis." Archives of Internal Medicine 132.6 (1973): 854-860.
Colice, Gene L., et al. "Medical and surgical treatment of parapneumonic effusions: an evidence-based guideline." CHEST Journal 118.4 (2000): 1158-1171.
Villena, Victoria, et al. "Clinical implications of appearance of pleural fluid at thoracentesis." Chest 125.1 (2004): 156-159.