Adenosine Deaminase (ADA)
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Evaluating tuberculosis (TB) in body fluids
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🧪 Adenosine Deaminase (ADA) Test
Aspect | Details |
|---|---|
Fasting Required? | ❌ Not required |
Sample Type | Body fluids: Pleural fluid, peritoneal fluid, CSF, sometimes blood |
Main Organs Involved | Immune system, lungs, peritoneum, brain (if TB meningitis suspected) |
Primary Use | Detect tuberculosis infection in body cavities |
🧬 What is ADA?
- Adenosine deaminase (ADA) is an enzyme involved in purine metabolism and is essential for the proliferation and differentiation of lymphocytes, especially T cells.
- Elevated ADA levels in body fluids indicate active cellular immune response, commonly seen in tuberculosis.
🧠 Clinical Importance
Test Use | Why It’s Done |
|---|---|
✅ TB Pleural Effusion diagnosis | ADA in pleural fluid helps differentiate TB from non-TB effusions |
🧪 TB Peritonitis or Meningitis | ADA levels in ascitic or CSF samples aid early TB diagnosis |
🔍 Alternative to culture | Faster and less invasive than AFB culture or PCR |
📈 Interpretation of ADA Levels
ADA Level (U/L) | Interpretation |
|---|---|
< 30 | Usually not TB-related; consider other causes |
> 40–45 | Suggestive of tuberculous effusion |
> 60 | Highly suggestive of TB, especially with lymphocyte predominance |
False Positives | Empyema, rheumatoid pleuritis, malignancy, lymphoma |
⚠️ Important: ADA must be interpreted with clinical findings and fluid cytology.
🧪 Recommended Conjunction Tests
Test | Why It’s Done |
|---|---|
AFB Staining & Culture | Confirms presence of mycobacteria |
GeneXpert (CBNAAT) | Detects TB DNA and rifampicin resistance |
PCR for MTB | Molecular confirmation of Mycobacterium tuberculosis |
Pleural/Ascitic Fluid Cytology | Helps differentiate TB from malignancy |
ESR & CRP | General inflammation markers |
Chest X-ray / Ultrasound / CT | Supports diagnosis of TB involvement in body cavities |
⚠️ Limitations of ADA Test
Limitation | Explanation |
|---|---|
Not specific to TB | Elevated in some cancers, empyema, and autoimmune diseases |
Does not detect organism | Confirms immune response, not direct presence of TB |
Age-related variation | ADA levels may be higher in children than adults |
✅ Summary Table
Test | ADA (Adenosine Deaminase) |
|---|---|
Main Use | Supportive diagnosis of extrapulmonary TB |
Sample Type | Pleural fluid, ascitic fluid, CSF, blood |
Normal Range | Typically <30 U/L (varies by lab and fluid type) |
Elevated In | TB, lymphoma, autoimmune pleuritis, some cancers |
Used With | AFB smear, GeneXpert, cytology, imaging |
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