Adenosine Deaminase (ADA)

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Adenosine Deaminase (ADA) Test Information Guide

Why is it done?
- Measures the enzyme adenosine deaminase, which breaks down the purine metabolite adenosine in blood and body tissues
- Diagnose adenosine deaminase deficiency (ADA-SCID), a form of severe combined immunodeficiency affecting T cell, B cell, and NK cell development
- Screen newborns for ADA deficiency as part of expanded newborn screening programs
- Evaluate patients with recurrent infections and immunodeficiency
- Monitor purine metabolite accumulation (deoxyadenosine, deoxyadenosine triphosphate) in blood and urine
- Assess immunological status and lymphocyte function in patients with recurrent infections
- Performed within first days of life (newborn screening) or when immunodeficiency is suspected
Normal Range
- Red Blood Cells (RBC): 22–42 units/g hemoglobin or 40–100 nmol/min/mL RBCs
- Plasma/Serum: 5–15 units/L or 0.08–0.25 μmol/min/mL
- Normal values may vary slightly between laboratories based on methodology and population
- Negative/Normal Result: Indicates normal ADA enzyme activity, suggesting absence of ADA deficiency
- Low/Abnormal Result: ADA activity significantly below normal range (typically <5% of normal), consistent with ADA deficiency
- Elevated deoxyadenosine or deoxyadenosine triphosphate (dATP) levels accompany low ADA activity
- Borderline values require repeat testing and correlation with clinical symptoms
Interpretation
- Severely Deficient (<1% activity): Classic ADA-SCID presentation; profoundly reduced ADA enzyme activity in RBCs and plasma; rapid accumulation of toxic metabolites (deoxyadenosine, dATP) leading to T cell death
- Partial Deficiency (1–10% activity): Atypical ADA-SCID or delayed-onset ADA-SCID; some residual enzyme activity present; variable clinical presentation ranging from early onset to late-onset disease
- Normal Activity: Effectively rules out ADA deficiency; indicates adequate metabolic clearance of adenosine and deoxyadenosine
- RBC vs Plasma Levels: RBC ADA levels are more clinically relevant than plasma; RBCs accumulate deoxyadenosine more readily; plasma ADA may be falsely elevated in hemolyzed samples
- Metabolite Testing: Elevated deoxyadenosine and dATP levels in plasma and urine support diagnosis; dATP accumulation in lymphocytes is most toxic to T cells
- Factors Affecting Results: Recent blood transfusion (dilutes ADA levels), hemolysis during collection, hemoglobin variants, age (slight activity changes in newborns), medications affecting purine metabolism
- Clinical Correlation: ADA levels must be interpreted with clinical presentation (recurrent infections, failure to thrive, developmental delay); genetic testing for ADA mutations confirms diagnosis
Associated Organs
- Primary Organ Systems: Immune system (thymus, lymph nodes, spleen), lymphocytes (T cells most severely affected)
- Secondary Involvement: Central nervous system (developmental delay, neurological symptoms in late-onset disease), liver (hepatosplenomegaly), skeletal system (skeletal dysplasia in some cases)
- Adenosine Deaminase Deficiency (ADA-SCID): Severe combined immunodeficiency characterized by absent or severely reduced T cell, B cell, and NK cell populations; represents approximately 10–15% of SCID cases
- Atypical/Partial ADA Deficiency: Delayed-onset disease presenting later in infancy or childhood; progressive immunodeficiency with recurrent opportunistic infections
- Clinical Manifestations: Recurrent bacterial, viral, and fungal infections; failure to thrive; chronic diarrhea; developmental delay; hepatosplenomegaly; adenopathy; lymphoid hypoplasia
- Toxic Metabolite Effects: dATP accumulation specifically toxic to lymphocytes; ribonucleotide reductase inhibition prevents DNA synthesis; adenosine toxicity impairs cell survival and proliferation
- Potential Complications: Life-threatening infections (Pneumocystis jirovecii, cytomegalovirus, mycobacteria); autoimmune manifestations; malignancy risk; metabolic complications; neurological sequelae in atypical forms
Follow-up Tests
- Genetic Testing: DNA sequencing for ADA gene mutations (chromosome 20q13.11); confirms diagnosis and identifies specific defects
- Metabolite Analysis: Plasma and urine deoxyadenosine, deoxyadenosine triphosphate (dATP), and adenosine levels; increased metabolite levels correlate with disease severity
- Immunological Assessment: Complete blood count (CBC) with differential; T cell, B cell, and NK cell enumeration (flow cytometry); lymphocyte subset analysis
- Lymphocyte Function Tests: T cell proliferation assays; mitogen response testing; immune function evaluation to assess severity of immunodeficiency
- Deoxynucleotide Triphosphate Profiles: dATP and dGTP measurements; important for monitoring toxicity and treatment response
- Purine Metabolite Panel: Comprehensive analysis of adenosine, inosine, uric acid, and other purine metabolites
- Other SCID Enzyme Testing: PNP (purine nucleoside phosphorylase), RAG1/RAG2, IL7R, adenosine deaminase 2 (ADA2) to differentiate from other forms of SCID
- Infectious Disease Workup: If ADA deficiency confirmed, screen for active infections (viral serology, bacterial/fungal cultures); chest imaging for pneumonia or lymphoid tissue assessment
- Monitoring Frequency: For diagnosed ADA deficiency, repeat metabolite testing every 3–6 months during early management; more frequent during enzyme replacement or gene therapy; ongoing monitoring for treatment efficacy and complications
- Family Screening: Siblings and relatives of affected patients should be screened during newborn period or when symptoms develop
Fasting Required?
- Fasting: No – Fasting is not required for ADA testing
- Sample Type: Whole blood (EDTA tube) for RBC ADA testing; serum or plasma for enzyme assays; dried blood spot (DBS) for newborn screening
- Specimen Handling: Blood samples should be kept at room temperature and transported promptly (within 24–48 hours) to laboratory; hemolyzed samples should be avoided as they affect ADA level accuracy
- Special Instructions: Recent blood transfusions should be noted (dilutes ADA levels); inform laboratory of any recent transfusions within 3 months
- Medications: No medications need to be discontinued; inform laboratory of any medications (particularly immunosuppressive agents or purine analogs like deoxycoformycin) that may affect results
- Patient Preparation: Newborns should have blood collected via heel prick onto filter paper cards (dried blood spot); older children and adults via routine venipuncture (no special preparation needed)
- Timing Considerations: For newborn screening, sample should be collected 24–48 hours after birth; for diagnostic testing in older patients, any time of day is acceptable

How our test process works!