From the Guidelines
A connective tissue disease (CTD) blood test checks for specific autoantibodies, including antinuclear antibodies (ANA), anti-double-stranded DNA (anti-dsDNA), and anti-extractable nuclear antigens (anti-ENA), to diagnose autoimmune disorders affecting connective tissues throughout the body. These tests are crucial in identifying conditions such as systemic lupus erythematosus, rheumatoid arthritis, scleroderma, Sjögren's syndrome, polymyositis, and mixed connective tissue disease 1. The detection of ANA is considered the first level test for laboratory diagnosis of systemic autoimmune rheumatic diseases (SARD) 1.
Key Autoantibodies Tested
- Antinuclear antibodies (ANA)
- Anti-double-stranded DNA (anti-dsDNA)
- Anti-extractable nuclear antigens (anti-ENA)
- Other specific antibodies like anti-Smith, anti-Ro/SSA, anti-La/SSB, anti-Scl-70, anti-centromere, and anti-Jo-1 antibodies
Importance of Clinical Context
It's essential to interpret positive results alongside clinical symptoms, as some healthy individuals may have low levels of these antibodies without disease 1. The test requires a simple blood draw, and results typically take several days to process. These autoantibodies develop when the immune system mistakenly attacks the body's own tissues, particularly components of connective tissue that provide structure and support throughout the body.
Testing Recommendations
The international recommendations for the assessment of autoantibodies to cellular antigens referred to as anti-nuclear antibodies suggest that ANA, anti-dsDNA, and anti-ENA testing should be included in the autoantibodies detection as part of the diagnostic work-up of SARD as well as some other autoimmune diseases 1. Additionally, testing for anti-dsDNA antibodies is advised when there is clinical suspicion of systemic lupus erythematosus (SLE) 1.
Methodology
The indirect immunofluorescent assay (IIFA) is the reference method for ANA screening, and alternative assays can be used while keeping in mind that false negative and false positive ratios of these methods may be different 1. Each laboratory should verify the recommended cut-off for kits used to determine ANA, anti-dsDNA, and anti-ENA antibodies 1.
From the Research
Connective Tissue Disease Blood Test
A connective tissue disease (CTD) blood test checks for various autoantibodies and biomarkers associated with CTDs, including:
- Antinuclear antibodies (ANAs) [ 2, 3 ]
- Anti-double-stranded DNA (anti-dsDNA) antibodies [ 4, 3 ]
- Antinucleosome antibodies [ 4 ]
- Specific autoantibodies such as antibodies to Sm, SSA/Ro60, U1RNP, topoisomerase I, centromere protein B (CENPB), RNA polymerase III, and Jo1 [ 3 ]
Purpose of the Test
The purpose of a CTD blood test is to:
- Aid in the diagnosis of CTDs such as systemic lupus erythematosus, systemic sclerosis, myositis, Sjögren's syndrome, and rheumatoid arthritis [ 2, 5 ]
- Monitor disease activity and progression [ 5 ]
- Support the classification of CTDs [ 3 ]
- Help clinicians in making a proper rheumatological diagnosis [ 6 ]
Interpretation of Test Results
The interpretation of CTD blood test results requires: