Final answer:
A high-risk parapneumonic effusion is identified by a pH below 7.2, glucose below 60 mg/dL, LDH greater than two-thirds the upper limit of normal, and the presence of bacteria in the effusion.
Step-by-step explanation:
The question is regarding the characteristics that typify a high-risk parapneumonic effusion (empyema), which is a collection of pus in the pleural space, often due to pneumonia. The specific criteria for identifying a high-risk effusion include a pH below 7.2, suggesting an acidic environment; a glucose concentration below 60 mg/dL, indicative of decreased pleural fluid glucose relative to serum glucose due to bacterial consumption or decreased transport; an LDH (lactate dehydrogenase) level greater than two-thirds of the upper limit of normal, reflecting increased cellular turnover and necrosis; and the presence of bacteria in the effusion, which can be seen with Gram stain or culture. These criteria help clinicians in the diagnosis and management of empyema, guiding decisions regarding the need for more aggressive treatments such as chest tube placement or surgery.