Basic Autoimmune Tests for Initial Diagnosis
The diagnosis of systemic autoimmune diseases requires a panel of specific laboratory tests, including anti-nuclear antibodies (ANA), anti-double-stranded DNA (anti-dsDNA), and anti-extractable nuclear antigens (anti-ENA) antibodies as the fundamental first-line tests. 1
Core Initial Autoimmune Panel
Anti-Nuclear Antibodies (ANA)
- ANA testing is the first-level test and reference method for laboratory diagnosis of systemic autoimmune rheumatic diseases (SARD) 1
- Indirect immunofluorescence assay (IIFA) on HEp-2 cells remains the gold standard method for ANA detection 1
- A screening dilution of 1:160 is recommended as it provides better specificity while maintaining appropriate sensitivity 1
- Both nuclear and cytoplasmic patterns should be reported and specified when detected 1
Anti-Double-Stranded DNA (anti-dsDNA)
- Should be tested when ANA is positive and there is clinical suspicion of systemic lupus erythematosus (SLE) 1
- The Farr assay and Crithidia luciliae immunofluorescence test (CLIFT) offer high clinical specificity 1
- Provides important diagnostic and prognostic information for SLE 1
Anti-Extractable Nuclear Antigens (anti-ENA)
- Testing should follow a positive ANA result 1
- Common ENA specificities to test include:
- Anti-Ro/SSA (associated with SLE, Sjögren's syndrome)
- Anti-La/SSB (associated with Sjögren's syndrome, SLE)
- Anti-Sm (highly specific for SLE)
- Anti-RNP (associated with mixed connective tissue disease, SLE)
- Anti-Scl-70 (associated with systemic sclerosis)
- Anti-Jo-1 (associated with polymyositis/dermatomyositis) 1, 2
Disease-Specific Additional Testing
For Suspected Autoimmune Hepatitis
- Anti-smooth muscle antibodies (SMA)
- Anti-liver/kidney microsome type 1 (anti-LKM-1)
- Anti-liver cytosol type 1 (anti-LC1)
- Anti-soluble liver antigen/liver pancreas (anti-SLA/LP)
- Antimitochondrial antibodies (AMA) to exclude primary biliary cirrhosis 1
For Suspected Autoimmune Encephalitis
- CSF and serum neuronal autoantibodies panel
- Inflammatory markers in CSF (IgG index, oligoclonal bands) 1
For Suspected Vasculitis
- Antineutrophil cytoplasmic antibodies (ANCA)
- Perinuclear ANCA (p-ANCA) and cytoplasmic ANCA (c-ANCA) 1
Complementary Tests
- Complete blood count with differential
- Inflammatory markers (C-reactive protein, erythrocyte sedimentation rate)
- Complement components (C3, C4) - particularly important for SLE monitoring
- Immunoglobulin levels (IgG, IgA, IgM) 1, 3
- Rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies if arthritis is present 2, 3
Important Considerations
Testing Methodology
- Laboratory should specify the methods used for detecting autoantibodies when reporting results 1
- In-house assays should be standardized according to international standards 1
- Clinicians should develop a relationship with laboratory pathologists to investigate inconsistent or surprising results 4
Interpretation Caveats
- Autoantibody testing should only be performed in patients with reasonable clinical suspicion of autoimmune disease 4
- A positive ANA at low titers can be found in healthy individuals and should be interpreted in clinical context 1
- False negative results can occur with alternative methods to IIFA; if clinical suspicion is strong and alternative method is negative, IIFA should be performed 1
Follow-up Testing
- ANA testing is primarily intended for diagnostic purposes, not for monitoring disease progression 1
- Anti-dsDNA and complement levels may be useful for monitoring SLE disease activity 1, 3
- Repeated testing of stable markers should be avoided unless there is a significant change in clinical presentation 1, 4
By following this systematic approach to autoimmune testing, clinicians can efficiently establish diagnoses, assess prognosis, and make appropriate treatment decisions while avoiding unnecessary testing.