American Board of Internal Medicine (ABIM) Certification Practice Exam

According to Light's Criteria, what is the required value for pleural fluid total protein to serum total protein ratio to suggest an exudative pleural effusion?

1. Less than 0.5

2. Equal to 0.6

3. Greater than 0.5

4. Greater than 0.7

The correct answer is: Greater than 0.5

Light's Criteria is a set of guidelines used to differentiate between exudative and transudative pleural effusions based on specific biochemical characteristics of the pleural fluid compared to serum levels. One of the key parameters evaluated is the pleural fluid total protein to serum total protein ratio. A ratio greater than 0.5 indicates that the pleural effusion is likely to be exudative. This is significant because exudative effusions often suggest the presence of underlying disease processes, such as infection, malignancy, or inflammatory conditions, which typically require different management compared to transudative effusions that are often caused by systemic conditions like heart failure or cirrhosis. In clinical practice, identifying exudative effusions using Light's Criteria helps guide further diagnostic and therapeutic interventions. Therefore, the requirement for the pleural fluid total protein to serum total protein ratio being greater than 0.5 is a crucial criterion to remember when assessing pleural effusions.