Two list of ada false positives and negative table and pathophysiology of ada
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"adenosine deaminase" AND "tuberculosis"
Let me read the key textbook sections.
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pleural fluid adenosine deaminase false positive empyema rheumatoid lymphoma brucellosis false negative HIV elderly
I took "ADA" to mean adenosine deaminase, the TB marker in pleural, peritoneal and CSF fluid. If you meant the American Diabetes Association or another ADA, tell me.
Pathophysiology of ADA
Enzyme function. ADA (EC 3.5.4.4) is a purine salvage enzyme. It irreversibly deaminates adenosine and 2'-deoxyadenosine to inosine and 2'-deoxyinosine. - Tietz Textbook of Laboratory Medicine, 7th Ed, p. 3057-3058; - Henry's Clinical Diagnosis, ADA section
Why it rises in TB:
- ADA is a product of activated lymphocytes. It is especially abundant in T lymphocytes, which proliferate in tuberculosis. - Murray & Nadel's Respiratory Medicine; - Henry's
- M. tuberculosis triggers a delayed-type hypersensitivity response. CD4+ T cells and activated monocytes/macrophages accumulate in the serosal space (pleura, peritoneum, meninges, pericardium). ADA activity in the fluid rises with this cellular activity.
- There are two isoenzymes. ADA1 is found in lymphocytes and most cells. ADA2 comes mainly from monocytes and macrophages and is the isoform that rises in TB. This is from my own knowledge and is supported by the ADATPE study discussion. Isoenzyme testing is rarely available.
- Because the rise reflects the cellular response, ADA can also rise in neutrophilic effusions and in other lymphoproliferative or immune-driven states.
Typical cut-offs:
- Pleural fluid: about 35 to 40 U/L. A low value (<40 U/L) helps exclude TB because the test is highly sensitive.
- Ascitic fluid: about 36 to 40 IU/L, with an optimal cut-off of 39. Sensitivity was 100% and specificity 97% in a meta-analysis of 12 studies. - Yamada's Textbook of Gastroenterology
- CSF: ADA is a sensitive and specific test for TB meningitis. - Henry's
Other disease links. Inherited ADA deficiency causes SCID. Dysfunctional T and B cells result from accumulation of dATP and dGTP, which inhibit ribonucleotide reductase and deplete DNA precursors. - Harper's Illustrated Biochemistry, 32nd Ed. A rare inherited increase in red cell ADA depletes ATP and causes nonspherocytic hemolytic anemia. - Tietz
Table 1: False-positive ADA (high ADA, not TB)
| Cause | Mechanism / comment |
|---|---|
| Empyema / complicated parapneumonic effusion | Dense neutrophil and lymphocyte infiltrate. In one study ADA was above 35 U/L in up to 40% of parapneumonic effusions. - Murray & Nadel's |
| Lymphoma | Proliferating lymphoid cells. About half of lymphoma effusions exceeded the cut-off. - Murray & Nadel's |
| Malignant effusion (carcinoma, mesothelioma) | Lymphocytic reaction. Less common. |
| Rheumatoid pleurisy / collagen vascular disease | Activated T cells and macrophages |
| IgG4-related pleural disease | Lymphoplasmacytic infiltrate. - Murray & Nadel's |
| Brucellosis, other intracellular infections (e.g., nocardiosis, some fungal) | Granulomatous, T-cell-driven response. From my knowledge; not confirmed in the retrieved sources. |
| Low-prevalence TB setting | Specificity falls and positive predictive value drops, so more false positives. - SA audit of high pleural ADA |
Very high ADA should raise suspicion of empyema or lymphoma. The Porcel series of over 2100 patients found this.
Table 2: False-negative ADA (low ADA, TB present)
| Cause | Mechanism / comment |
|---|---|
| Elderly patients | Blunted cell-mediated response. - Murray & Nadel's |
| Critically ill patients | Impaired immune response. - Murray & Nadel's |
| Advanced HIV / low CD4 count | Fewer T cells to produce ADA. Evidence conflicts: Murray & Nadel's says ADA remains sensitive in HIV, while Henry's notes limited utility in HIV neurologic disorders. |
| Other immunosuppression (steroids, biologics, malignancy) | Same mechanism. From my knowledge. |
| Early disease or low-lymphocyte effusion | Cell recruitment not yet established. From my knowledge. |
| Cirrhosis with TB peritonitis | One retrospective study suggested lower sensitivity. Other systematic reviews did not confirm this. - Yamada's |
| Hemorrhagic or paucicellular fluid; delayed or poorly handled sample | From my knowledge; not confirmed in the retrieved sources. |
How to use this clinically
- Use ADA alongside fluid lymphocyte predominance, clinical picture, culture, Xpert and biopsy. Do not use it alone.
- A low ADA excludes TB reliably only in immunocompetent patients with a low pretest probability.
- A high ADA in a neutrophilic effusion points toward empyema first, although TB can also cause neutrophilic effusions.
Recent evidence check
A PubMed search of the last 2 years found 3 recent meta-analyses. None contradict the textbook picture:
- PMID 41747349: IL-27 vs ADA for tuberculous pleural effusion.
- PMID 42074437: serum ADA in pulmonary TB.
- PMID 38494302: synovial fluid ADA in TB arthritis.
I did not read their full text. If you want a one-page printable version or a pleural-fluid diagnostic algorithm, I can make one.
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