Pleural Fluid ADA Levels

Function

Adenosine Deaminase (ADA) is an enzyme involved in purine metabolism. It is primarily found in T-lymphocytes, and its activity increases significantly during a cellular immune response. In the context of pleural fluid (the fluid between the layers of the tissue that line the lungs and chest cavity), measuring ADA levels is a rapid and non-invasive way to screen for specific inflammatory or infectious processes, most notably Tuberculosis (TB).

Why it is Ordered

ADA testing is ordered when a patient has a pleural effusion (excess fluid around the lungs) of unknown origin. It is particularly useful in regions where Tuberculosis is prevalent or when traditional TB tests (like sputum smears) are negative. It helps clinicians differentiate between different causes of fluid accumulation without immediately resorting to a pleural biopsy.

Associated Conditions

• Tuberculous Pleurisy: High ADA levels are highly suggestive of TB involvement in the pleura. It has a high sensitivity for this condition.
• Empyema: Bacterial infections that result in pus in the pleural space can cause very high ADA levels.
• Malignancy: Certain types of lung cancer or lymphomas can moderately elevate ADA.
• Rheumatoid Pleuritis: Autoimmune conditions affecting the lungs can cause increased lymphocyte activity and subsequent ADA elevation.
• Parapneumonic Effusions: Fluid buildup secondary to pneumonia.

ADA is a 'rule-in' test; while a low level strongly suggests TB is unlikely, a high level requires further investigation to confirm the specific cause.