Antinuclear Antibody (ANA) Test
Antinuclear Antibody (ANA) Test
Key Points
- Primary screening test for autoimmune disorders
- Detects antibodies targeting nuclear antigens
- Essential in pediatric rheumatology evaluation
- High sensitivity for SLE diagnosis (95-99%)
- Results expressed as titers with patterns
Overview
The ANA test is a fundamental diagnostic tool in pediatric rheumatology that detects autoantibodies targeting various nuclear antigens. These antibodies serve as crucial biomarkers for several autoimmune conditions, particularly systemic lupus erythematosus (SLE).
Diagnostic Value
- Primary screening for:
- Systemic Lupus Erythematosus (SLE)
- Mixed Connective Tissue Disease
- Juvenile Idiopathic Arthritis
- Systemic Sclerosis
- Sjögren's Syndrome
Clinical Indications
- Unexplained fever
- Joint pain or swelling
- Unexplained rash
- Raynaud's phenomenon
- Muscle weakness
- Persistent fatigue
- Multi-system involvement
Testing Methods
Indirect Immunofluorescence (IIF)
- Gold standard method
- Uses HEp-2 cells as substrate
- Reports both titer and pattern
- Sensitivity: 95-99%
- Specificity: 57-75%
Enzyme-Linked Immunosorbent Assay (ELISA)
- Automated screening method
- Quantitative results
- Higher throughput
- Lower sensitivity than IIF
Result Interpretation
Titer Interpretation
- Negative: <1:40
- Borderline: 1:40
- Positive: ≥1:80
- Strong positive: ≥1:160
Common Patterns and Associations
- Homogeneous: SLE, drug-induced lupus
- Speckled: Mixed connective tissue disease, SLE
- Nucleolar: Systemic sclerosis
- Centromere: Limited systemic sclerosis
- Peripheral: SLE
False Positives
- Viral infections
- Certain medications
- Chronic inflammatory conditions
- Healthy individuals (5-15%)
Clinical Practice Guidelines
- Initial Evaluation:
- Complete history and physical examination
- Document specific symptoms suggesting autoimmune disease
- Consider family history of autoimmune conditions
- Follow-up Testing:
- Anti-dsDNA
- Anti-Smith
- Anti-RNP
- Complement levels (C3, C4)
Monitoring
- Serial testing not recommended for monitoring disease activity
- Changes in titer do not correlate well with disease severity
- Focus on specific antibodies and clinical symptoms for monitoring
