The Adenosine Deaminase (ADA) - Synovial Fluid Test measures the level of the enzyme adenosine deaminase in the synovial fluid (the fluid that lubricates joints). 🔬 What is Adenosine Deaminase (ADA)? ADA is an enzyme involved in purine metabolism. It plays a critical role in the development and function of the lymphatic system, particularly T-lymphocytes (T-cells). Elevated ADA levels are typically found in conditions involving activated lymphocytes, especially in the presence of cell-mediated immune responses. 💧 Synovial Fluid Synovial fluid is a viscous fluid found in the cavities of movable joints. Its main function is to reduce friction between the articular cartilages of synovial joints during movement. Analysis of synovial fluid is crucial for diagnosing various joint diseases. 🩺 Clinical Significance of ADA in Synovial Fluid The primary clinical utility of measuring ADA in synovial fluid is in the diagnosis of tuberculous arthritis. Tuberculous Arthritis: This is a form of extrapulmonary tuberculosis where Mycobacterium tuberculosis infects a joint, leading to inflammation and destruction. It's often difficult to diagnose because the bacterial load in synovial fluid can be low, making traditional cultures challenging. High ADA levels (typically >30-40 IU/L) in synovial fluid are strongly suggestive of tuberculous arthritis. The influx and activation of lymphocytes (especially T-cells) at the site of infection cause the release of ADA. It is considered a reliable marker, especially when considered in conjunction with clinical symptoms and radiological findings. Differentiating from other arthropathies: Septic Arthritis (Non-Tuberculous): Bacterial arthritis caused by other bacteria (e.g., Staphylococcus aureus) usually does not significantly elevate ADA levels in synovial fluid. Rheumatoid Arthritis & Osteoarthritis: ADA levels are typically normal or only mildly elevated in these conditions, helping to rule out tuberculosis. Crystal-induced Arthritis (Gout, Pseudogout): ADA levels are generally normal.