What this test measures
Adenosine deaminase (ADA) is an enzyme of purine metabolism, particularly active in T lymphocytes and macrophages. When these cells are activated — as in tuberculous infection — ADA is released into the surrounding fluid. ADA measurement in a body fluid (pleural fluid most commonly; also ascitic, cerebrospinal and pericardial) is a useful adjunct in suspected tuberculous involvement, especially in settings where culture takes weeks and biopsy is invasive.
Pleural ADA is the most established use: in a high-TB-prevalence country like India, an exudative lymphocyte-predominant pleural effusion with ADA >40 U/L is strongly suggestive of tuberculous pleurisy. Serum ADA can also rise in TB but is less specific.
Why it matters
India has the world's highest TB burden, and extrapulmonary TB — pleural, peritoneal, meningeal, pericardial — accounts for ~15–20% of cases. Sputum testing is irrelevant for these forms, and pleural / CSF culture takes weeks with low sensitivity. ADA fills this diagnostic gap — a high ADA in the right clinical setting allows early empirical anti-TB therapy without waiting for culture.
Common Indian clinical scenarios — young adult with fever and pleural effusion (TB until proven otherwise); ascitic fluid in unexplained ascites; CSF in suspected tuberculous meningitis. ADA is not specific (lymphoma, parapneumonic effusion, empyema can also raise it) — it is interpreted with the full clinical picture, fluid analysis and Xpert MTB/RIF on the same fluid.
How to prepare
No patient preparation needed beyond the body-fluid sampling procedure (pleural tap, ascitic tap, lumbar puncture, pericardial tap). The fluid sample should be sent to the lab promptly and processed without delay — ADA can be measured on routine biochemistry analysers.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Pleural Fluid ADA (U/L)[1][2] | Pleural ADA <30 — TB unlikely · 30–40 grey zone · >40 — TB likely (in a lymphocytic exudate) | ADA <30 U/L in a lymphocytic exudate makes TB unlikely (high negative predictive value in high-prevalence settings). | Pleural ADA >40 U/L in a lymphocytic exudate strongly suggests tuberculous pleurisy. Sensitivity ~90%, specificity ~85–90% in high-TB-prevalence areas. False positives — empyema, lymphoma, rheumatoid pleural effusion, parapneumonic effusions. Add Xpert MTB/RIF on the same fluid and clinical correlation. |
| Ascitic Fluid ADA (U/L) | < 35 (TB unlikely); > 39 supports tuberculous peritonitis | Low ascitic ADA makes tuberculous peritonitis unlikely; consider other causes (cirrhosis, malignancy). | High ascitic ADA in a lymphocyte-predominant exudate (SAAG <1.1) supports tuberculous peritonitis — confirm with Xpert MTB/RIF and laparoscopy / biopsy if needed. |
| CSF ADA (U/L) | CSF ADA <10 — TB unlikely · >10 considered suggestive of TB meningitis | Low CSF ADA makes tuberculous meningitis less likely but does not exclude it; clinical and imaging context matters. | CSF ADA >10 U/L (with lymphocytic pleocytosis, high protein, low glucose) supports tuberculous meningitis. Cut-offs vary by lab. Confirm with CSF Xpert MTB/RIF and culture. |
ADA cut-offs in body fluids for TB
| Fluid | Suggestive ADA cut-off | Setting where useful |
|---|---|---|
| Pleural fluid | > 40 U/L (with lymphocytic exudate) | TB pleural effusion — most established use |
| Ascitic fluid | > 39 U/L (with SAAG <1.1) | TB peritonitis |
| CSF | > 10 U/L (varies by lab) | TB meningitis |
| Pericardial fluid | > 40 U/L | TB pericarditis |
| Serum | Not specific; not recommended | Limited utility |
Frequently asked questions
Why is ADA so useful in suspected TB?
Because mycobacterial cultures take 2–8 weeks and direct smear / Xpert sensitivity in pleural and CSF fluids is limited. A high ADA in a high-TB-prevalence country lets the clinician start empirical anti-TB therapy early, with confirmation following.
Do I need to fast?
No fasting is required for ADA testing.
What is the ADA cut-off for pleural TB?
In most labs, >40 U/L in a lymphocytic exudate strongly suggests tuberculous pleurisy. Cut-offs vary slightly (35–50) by method. <30 makes TB unlikely.
Can ADA be high in other diseases?
Yes — lymphoma, empyema, rheumatoid pleurisy, parapneumonic effusion, and (rarely) connective tissue disease can raise ADA. Interpretation requires clinical context and combining ADA with fluid cell counts, biochemistry and Xpert MTB/RIF.
Is ADA enough to diagnose TB?
It is a strong supportive marker but not a stand-alone diagnostic. Combine with clinical assessment, fluid analysis, Xpert MTB/RIF, imaging, and (where possible) biopsy / culture.
What about ADA in HIV-positive patients?
ADA can still rise in TB-HIV co-infection but the levels may be lower because of reduced T-cell responses in advanced HIV. Interpretation is harder and additional testing is important.
Is serum ADA useful?
Not really — serum ADA rises in many conditions (lymphoma, infection, autoimmune disease) and is non-specific. ADA is most useful when measured directly in the affected body fluid.
Related Other / Biochemistry tests
Tests commonly ordered alongside ADENOSINE DEAMINASE, or that help interpret an unexpected result.
Sources & references
- WHO — Tuberculosis Diagnosis and Treatment · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Tuberculous Pleural Effusion · accessed 2026-05-30T00:00:00.000Z
- ICMR — TB Diagnostic Algorithms · accessed 2026-05-30T00:00:00.000Z
- American Thoracic Society — Pleural Effusion Guidelines · accessed 2026-05-30T00:00:00.000Z
Book with Zelnoo
Get your ADENOSINE DEAMINASE test done at home — transparent prices, NABL-accredited labs.
Zelnoo lets you compare diagnostic test prices across NABL-accredited labs in Mumbai & Thane, book a free home phlebotomist visit, and receive digital reports in 24–48 hours into a consent-first report vault. No subscriptions, no membership fees — pay only for the test you book.
Book ADENOSINE DEAMINASE now