June 19, 2010

Q&A: Analysis of Pleural Effusion

A pleural effusion is excess fluid that accumulates in the pleural cavity, the fluid-filled space that surrounds the lungs. This excess fluid can impair breathing by limiting the expansion of the lungs.

This article is for Medical Students & Professionals
This is a Question & Answer revision article designed for medical students and professionals preparing for the PLAB, MRCP or USMLE examinations. They are based on actual questions from these examinations. You may find the Pneumonia article more useful, or one of our many articles on Diseases & Conditions, Medical Syndromes, Health & Wellness or Home Remedies.
In this article:
Pleural effusion and types
MCQ exam: clinical scenario
MCQ exam: answer
MCQ exam: explanation

Pleural effusion and types

A pleural effusion is an excessive accumulation of fluid in the pleural space. It can pose a diagnostic dilemma to the treating physician because it may be related to disorders of the lung or pleura, or to a systemic disorder.

Patients most commonly present with dyspnea, initially on exertion, predominantly dry cough, and pleuritic chest pain.

Various types of pleural effusion, depending on the nature of the fluid and what caused its entry into the pleural space, are hydrothorax (serous fluid), hemothorax (blood), urinothorax (urine), chylothorax (chyle), or pyothorax (pus) commonly known as pleural empyema. In general, the type of pleural effusion are:
  • Transudative. This pleural effusion fluid is similar to the fluid you normally have in your pleural space. It forms from liquid leaking across normal pleura. This type rarely needs to be drained unless it's very large. Congestive heart failure is the most common cause of this type.
  • Exudative. This forms from extra liquid, protein, blood, inflammatory cells or sometimes bacteria that leak across damaged blood vessels into the pleura. You may need to get it drained, depending on its size and how much inflammation there is. The causes of this type include pneumonia and lung cancer.
To treat pleural effusion appropriately, it is important to determine its etiology. However, the etiology of pleural effusion remains unclear in nearly 20% of cases. Thoracocentesis should be performed for new and unexplained pleural effusions. Laboratory testing helps to distinguish pleural fluid transudate from an exudate.

MCQ exam: clinical scenario

A 65 year old smoker with a three month history of a dry cough develops bilateral pleural effusions. Thoracocentesis reveals a pleural effusion with a Lactic Acid Dehydrogenase level which is less than 50% of the serum Lactic Acid Dehydrogenase level.

This suggests that:

a) the patient is probably diabetic
b) the patient is likely to have an empyema
c) the protein content of the effusion is likely to be above 4 g/dl
d) the specific gravity of the fluid is likely to be less than 1.02
e) the patient is likely to have a bronchogenic neoplasm

MCQ questions & answers on medicalnotes.info

MCQ exam: answer

The correct answer is D

MCQ exam: explanation

A Pleural fluid LDH-to-serum LDH ratio <0.6 is suggestive of a transudate. Laboratory differentiation of pleural fluid:
  • Specific gravity. Under 1.016 is suggestive of a transudate.
  • Protein. Less than 3 g/dl is suggestive of a transudate.
  • Pleural fluid protein-to-serum protein ratio. <0.5 is suggestive of a transudate.
  • Pleural fluid LDH-to-serum LDH ratio. <0.6 is suggestive of a transudate.
The pleural fluid level is not useful in the differential diagnosis of exudative pleural effusion.

Nevertheless, it is recommended that a pleural fluid LDH level be measured every time a diagnostic thoracentesis is performed, since the level of LDH in the pleural fluid is a good indicator of the degree of inflammation in the pleural space.

If the pleural fluid LDH level increases with serial thoracentesis, the degree of inflammation is worsening and one should be more aggressive in pursuing the diagnosis.

1). U.S. National Library of Medicine: Pleural effusion: diagnosis, treatment, and management. Available online: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753987/
2). WebMD: https://www.webmd.com/lung/pleural-effusion-symptoms-causes-treatments. Accessed Available online: https://www.webmd.com/lung/pleural-effusion-symptoms-causes-treatments

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