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🧪 ADA (Adenosine Deaminase) – CSF (Cerebrospinal Fluid)

Parameter	Details
Fasting Required?	❌ Not required
Sample Type	CSF (collected via lumbar puncture/spinal tap)
Primary Organ Involved	Central Nervous System (CNS) – especially meninges
Primary Purpose	Supportive diagnosis of Tuberculous Meningitis (TBM)

🔬 What is ADA?

ADA is an enzyme critical for T-cell–mediated immunity.
In TBM, the immune response in the CSF leads to increased ADA levels due to lymphocyte activation.
ADA testing offers rapid, supportive evidence in resource-limited or high TB-burden settings.

🧠 Why Test ADA in CSF?

ADA in CSF helps to:

Differentiate TB meningitis from viral or bacterial meningitis.
Provide early presumptive diagnosis when AFB culture or GeneXpert may be negative or delayed.
Guide urgent treatment decisions in high-risk, critically ill patients.

📈 Interpretation of ADA in CSF

ADA Level (U/L)	Interpretation
< 5 U/L	TBM unlikely
5–10 U/L	Borderline; interpret with clinical and CSF findings
> 10 U/L	Suggestive of Tuberculous Meningitis, especially with lymphocytes
> 15–20 U/L	Strongly supportive of TBM (especially in high-prevalence regions)

⚠️ ADA should not be used alone for diagnosis — CSF glucose, protein, and cell count are essential.

🧪 Recommended Conjunction Tests

Test	Purpose
CSF Cell Count & Differential	TBM often shows lymphocytic pleocytosis
CSF Protein & Glucose	Elevated protein and low glucose are classical TB findings
CSF AFB Staining & Culture	Gold standard, but low sensitivity & slow
CSF GeneXpert / CBNAAT	Rapid molecular confirmation of Mycobacterium tuberculosis
MRI Brain with Contrast	Detect basal meningeal enhancement, hydrocephalus
ESR / CRP / Mantoux test	General indicators of TB and inflammation

⚠️ Limitations & Considerations

Limitation	Explanation
ADA is not specific	Elevated in fungal infections, lymphoma, or autoimmune diseases
False negatives in immunosuppressed	Especially in HIV-positive or steroid-treated patients
Best used as supportive evidence	Not a replacement for microbiological confirmation

✅ Summary Table

Test Name	ADA – Cerebrospinal Fluid (CSF)
Main Use	Support diagnosis of Tuberculous Meningitis (TBM)
Sample Type	CSF via lumbar puncture
Significant Levels	>10 U/L suggestive; >15 U/L strongly supportive
Conjunction Tests	CSF AFB, GeneXpert, cell count, glucose, protein, MRI
Interpretation Caveats	Should be used with full CSF profile and clinical context

Adenosine Deaminase (ADA)(CSF)