American Board of Internal Medicine (ABIM) Certification Practice Exam

What finding on pH indicates a complicated pleural effusion?

1. pH less than 7.0

2. pH less than 7.2

3. pH greater than 7.4

4. pH around 7.2

The correct answer is: pH less than 7.2

A pH of less than 7.2 in a pleural effusion is indicative of a complicated pleural effusion, often associated with conditions such as pneumonia, empyema, or malignancy. In this context, a lower pH level reflects a more acidic environment in the pleural space, which can result from the presence of bacteria or necrotic tissue that produces lactic acid, or from an influx of inflammatory cells. A pH below 7.2 is significant because it suggests that the pleural effusion is not just a transudate — which typically has a higher pH — but rather a complex process, potentially involving infection or malignancy that may lead to further complications requiring intervention. Understanding the significance of pH in pleural effusions is crucial for appropriate clinical management and decision-making regarding further diagnostic workup or therapeutic procedures. Hence, recognizing a pH value in this specific range provides key insights into the nature and potential complications of the effusion.