## **Core Concept**
The glucose level in pleural effusion is an important diagnostic tool. A low glucose level in pleural effusion, often defined as less than 60 mg/dL, is associated with certain 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) typically presents with a low glucose level in the pleural fluid due to the inflammatory process and the high metabolic rate of the tuberculous infection. Similarly, rheumatoid arthritis (Option B) and empyema (Option C) can cause low glucose levels in pleural effusions due to the intense inflammatory response and bacterial infection, respectively. However, **transudative pleural effusions**, which are caused by conditions like heart failure, liver cirrhosis, or nephrotic syndrome, usually have glucose levels similar to that of the serum because they result from hydrostatic pressure or oncotic pressure imbalances rather than an inflammatory process.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but based on common causes of low glucose in pleural effusions, conditions like complicated parapneumonic effusions or malignancies could be associated with low glucose levels.
- **Option B:** Rheumatoid arthritis can cause low glucose levels in pleural effusions due to the high metabolic rate of the inflammatory cells.
- **Option C:** Empyema, which is pus in the pleural space, usually results from a bacterial infection and can lead to low glucose levels due to bacterial consumption and the inflammatory response.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that a low glucose level in pleural effusion (<60 mg/dL) often points towards an **exudative** process, which includes conditions like empyema, tuberculous pleurisy, rheumatoid pleurisy, and malignant pleural effusions. This differentiates them from **transudative** effusions, which typically have normal glucose levels. ## **Correct Answer:** . Transudative pleural effusion