Pleural Fluid For Culture And Sensitivity

Function

The pleural space is the thin gap between the lungs and the chest wall, containing a small amount of lubricating fluid. When an infection or inflammatory process occurs, fluid can accumulate (pleural effusion). Analyzing this fluid through culture and sensitivity is the gold standard for identifying the causative agent of an infection within that space.

Why it is Ordered

This test is ordered when a patient presents with a pleural effusion and clinical signs of infection (fever, chest pain, productive cough). It is used to differentiate between a simple parapneumonic effusion (fluid associated with pneumonia) and an empyema (pus in the pleural space). Identifying the specific pathogen allows for targeted antibiotic therapy and determines if surgical drainage is necessary.

Associated Conditions

• Empyema: A collection of pus in the pleural cavity, often requiring aggressive drainage.
• Bacterial Pneumonia: The most common precursor to infected pleural fluid.
• Tuberculosis: TB can cause chronic pleural effusions that require specialized culture media.
• Fungal Pleuritis: Rare, but seen in immunocompromised individuals.

Diagnostic Process

The fluid is obtained via thoracentesis (needle aspiration). In the lab, it is placed on various agar plates to grow aerobic and anaerobic bacteria. If growth occurs, the sensitivity portion determines which antibiotics can penetrate the pleural space and kill the bacteria.