Adenosine Deaminase (ADA) Test (Synovial Fluid)
The Adenosine Deaminase (ADA) test in synovial fluid is a diagnostic tool used primarily to assess the presence of tuberculosis (TB) arthritis. Elevated levels of ADA in synovial fluid can indicate an active TB infection, helping differentiate it from other types of arthritis.
Adenosine Deaminase (ADA) is an enzyme that catalyzes the metabolism of purines, specifically in the conversion of adenosine to inosine. It therefore helps in maintaining the balance of nucleotides in cells, which is particularly important for the normal functioning of the immune system.
Indications for Adenosine Deaminase (ADA) test.
- Suspected Tuberculosis Arthritis: The test is indicated for patients with joint effusions and clinical symptoms suggestive of TB infection.
- Differential Diagnosis: It enables one to distinguish between TB arthritis and other forms of septic or inflammatory arthritis.
How is Adenosine Deaminase (ADA) test done?
Sample Collection
Synovial fluid obtained via arthrocentesis (joint aspiration). A minimum volume of approximately 1 mL is typically required. The sample should be kept sterile and transported at room temperature
Pleural effusion necessitates a chest drain procedure, which is performed by a skilled physician in a fully sterile environment. Sometimes a procedure called thoracentesis is used, in which a device is placed into the patient’s pleural space and fluid and air are aspirated.
The fluid is aspirated using paracentesis for ascitic effusion. It is also possible to aspirate the fluid from the synovial cavity and gather CSF.The drain tube site is cleaned with an antiseptic, and the sample is taken using aseptic technique.
For a serum sample, blood is obtained from the patient’s arm vein and placed in a sterile processing container.
Reference Values
Cut-off Levels
Studies suggest that ADA levels above 30 to 76 U/L may indicate TB arthritis, with varying sensitivities and specificities reported:
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- Sensitivity: Ranges from 83% to 100%
- Specificity: Ranges from 67% to 100%
Elevated ADA levels (>76 U/L) in the absence of bacterial culture growth are highly suggestive of TB arthritis.
How do you prepare for Adenosine Deaminase (ADA) test
The test does not require fasting. The patient is informed about the appropriate aspiration technique prior to sample collection. It is a straightforward bedside procedure for inpatients.
Clinical Significance
Adenosine Deaminase (ADA) is a clinically important enzyme with various implications in medical diagnostics and research. These include:
- Tuberculous Meningitis Diagnosis
ADA activity measurement in cerebrospinal fluid (CSF) is a valuable diagnostic marker for tuberculous meningitis, a severe form of tuberculosis affecting the central nervous system.
- Immune Deficiency Disorders
ADA deficiency, a rare genetic disorder resulting in low or absent ADA activity, leads to severe combined immunodeficiency (SCID.
- Autoimmune Diseases
ADA inhibitors, which block the activity of ADA, are used in the treatment of autoimmune diseases, particularly rheumatoid arthritis and psoriasis.
- Oncology
ADA activity may be measured in cancer research to assess its role in tumor development and progression.
- Lymphoproliferative Disorders
ADA levels may be elevated in some lymphoproliferative disorders; therefore, monitoring ADA levels in conjunction with other clinical assessments can be useful in the evaluation of these conditions.
- Research and Drug Development
Understanding ADA’s role in purine metabolism and immune regulation contributes to advances in medical science and therapeutic interventions. This is relevant for research related to immunology, genetics, and enzymes.
Treatment Approaches
- For Tuberculosis Arthritis: If the ADA test suggests tubercular arthritis, treatment typically involves anti-tuberculosis therapy (ATT), which includes isoniazid, rifampin, ethambutol, and pyrazinamide for several months.
- For Other Inflammatory Conditions: If elevated ADA levels indicate rheumatoid arthritis or another inflammatory condition, treatment may involve anti-inflammatory drugs, corticosteroids, or disease-modifying antirheumatic drugs (DMARDs).
- For ADA Deficiency: In rare cases, ADA deficiency can lead to severe combined immunodeficiency (SCID), which may require enzyme replacement therapy or gene therapy.
Turnaround Time
Results for the ADA test in synovial fluid are generally available within 4 hours to a few days, depending on the laboratory’s processing capabilities.
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