CSF ADA Levels

Function

Adenosine Deaminase (ADA) is an enzyme involved in purine metabolism. It is primarily found in T-lymphocytes and plays a crucial role in the immune response. When the central nervous system is affected by certain infections, particularly those that trigger a cellular immune response, the levels of ADA in the Cerebrospinal Fluid (CSF) rise.

Why it is Ordered

The CSF ADA test is most frequently used as a rapid screening tool for Tuberculous Meningitis (TBM). TBM is notoriously difficult to diagnose because traditional cultures for Mycobacterium tuberculosis can take weeks. ADA provides a much faster, albeit indirect, indication of infection. It is ordered when a patient presents with:

• Chronic headache and fever.
• Neck stiffness.
• Neurological deficits of unknown origin.

Associated Conditions

• Tuberculous Meningitis: High sensitivity and specificity for this condition.
• Bacterial Meningitis: Can cause moderate elevations.
• Neurobrucellosis: Another infectious cause of raised ADA.
• CNS Lymphoma: Non-infectious cause of significantly high ADA levels.

While ADA is a powerful tool, it must be interpreted alongside CSF glucose, protein, and cell counts to distinguish between tuberculosis and other types of meningitis.