ACP InternistMKSAP Quiz: Evaluation for Pneumonia

Which Pleural Fluid Test is Most Appropriate: Lactate Dehydrogenase, pH, Procalcitonin, or Total Protein?

An 81-year-old man is evaluated in the hospital for pneumonia. His physical examination reveals a temperature of 38.0 °C (100.4 °F), blood pressure of 119/65 mm Hg, pulse rate of 110/min, and respiration rate of 24/min. Oxygen saturation is 88% with the patient breathing ambient air. There are coarse rhonchi and decreased breath sounds and dullness to percussion over the left lower half of the chest. A CT scan of the chest shows left lower lobe consolidation and loculated left pleural effusion. A thoracentesis is performed.

The following tests are considered:

• Lactate dehydrogenase (LDH): An enzyme that can be elevated in various conditions, including inflammation and infection.
• pH: A measure of acidity or alkalinity. In the context of pleural fluid, a low pH can indicate a complicated parapneumonic effusion.
• Procalcitonin: A protein that can be elevated in bacterial infections, but its value in differentiating parapneumonic and tuberculous pleural effusions from other causes of exudative effusions is not established.
• Total protein: Useful in characterizing the pleural fluid as exudative by Light’s criteria (ratio of pleural-fluid protein to serum protein level >0.5).

Which of the pleural fluid tests do you think is most appropriate in directing therapy?

According to a study published in the American Journal of Respiratory and Critical Care Medicine, approximately 1.5 million people in the United States have a pleural effusion each year.

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