## Core Concept
The glucose level in pleural fluid can be used as a diagnostic tool to help differentiate between various causes of pleural effusions. A low glucose level in pleural fluid is often associated with conditions that lead to increased glucose consumption or impaired glucose transport into the pleural space.

## Why the Correct Answer is Right
Tuberculous pleurisy (Option D) is known to have a variable glucose level in pleural fluid, but it is one of the conditions where the glucose level can be low, though not as consistently low as in empyema or rheumatoid pleurisy. However, among the given options, tuberculous pleurisy relatively less frequently presents with very low glucose levels compared to the other conditions listed, which are more characteristically associated with low pleural fluid glucose.

## Why Each Wrong Option is Incorrect
- **Option A (Empyema):** Empyema, which is pus in the pleural space, usually results from a bacterial infection. The bacterial infection consumes glucose, leading to low glucose levels in the pleural fluid. Therefore, empyema is indeed associated with low glucose levels.
- **Option B (Rheumatoid Pleurisy):** Rheumatoid arthritis can cause pleurisy, and one of the characteristics of rheumatoid pleurisy is a low glucose level in the pleural fluid, often due to the inflammatory process consuming glucose.
- **Option C (Malignant Pleurisy):** Malignant pleurisy, resulting from metastasis of cancer to the pleura, can also lead to low glucose levels in the pleural fluid. The mechanism may involve high metabolic rates of tumor cells and inflammatory cells.

## Clinical Pearl / High-Yield Fact
A low glucose level (< 60 mg/dL) in pleural fluid is suggestive of complicated parapneumonic effusions, empyema, rheumatoid pleurisy, and tuberculous pleurisy. The differential diagnosis for pleural effusions with low glucose includes these conditions. A key point to remember is that while a low glucose level can help narrow down the differential diagnosis, it is not specific and must be interpreted in the context of clinical presentation, imaging, and other laboratory findings. ## Correct Answer: D. Tuberculous Pleurisy