⚕️ Educational content only. This article explains autoimmune laboratory tests from an immunology science perspective. It is not medical advice. Consult a healthcare professional for personal health concerns.
Autoimmune diseases occur when the immune system produces antibodies directed against the body’s own tissues. Laboratory immunology tests detect these autoantibodies in blood, helping clinicians diagnose and monitor conditions such as systemic lupus erythematosus (SLE), rheumatoid arthritis, vasculitis, and autoimmune thyroid disease.
Key Takeaways
- ANA (antinuclear antibody) is a sensitive screening test for SLE and other connective tissue diseases, but is non-specific.
- Anti-dsDNA is highly specific for SLE and correlates with disease activity and lupus nephritis.
- ANCA (antineutrophil cytoplasmic antibody) is associated with vasculitides including GPA and MPA.
- Rheumatoid factor (RF) and anti-CCP are used in the diagnosis of rheumatoid arthritis; anti-CCP is more specific.
Antinuclear Antibody (ANA)
ANA testing detects antibodies directed against nuclear antigens. It is performed by indirect immunofluorescence (IIF) on HEp-2 cells, which gives a titre (e.g. 1:80, 1:160, 1:320) and a pattern (homogeneous, speckled, nucleolar, centromere). A positive ANA at a titre of ≥1:160 is considered significant. ANA is positive in >95% of SLE patients, making it a sensitive screening test, but it is also positive in other connective tissue diseases (Sjögren’s, scleroderma, myositis), and in up to 15–20% of healthy individuals at low titres. Positive ANA should trigger reflex testing for specific extractable nuclear antigens (ENAs) and anti-dsDNA.
Anti-dsDNA
Antibodies against double-stranded DNA are highly specific for SLE (>99% specificity). They are included in the ACR/EULAR classification criteria for SLE. Anti-dsDNA levels fluctuate with disease activity — rising levels often precede lupus nephritis flares, making serial monitoring clinically useful. Testing methods include Crithidia luciliae IIF (which detects high-avidity antibodies and is highly specific) and ELISA (more sensitive but less specific).
ENA Panel (Extractable Nuclear Antigens)
ENA testing detects antibodies against specific nuclear proteins. Key antigens include: anti-Ro/SSA and anti-La/SSB (Sjögren’s syndrome and neonatal lupus); anti-Sm (SLE-specific, though insensitive); anti-Scl-70 / anti-topoisomerase I (diffuse scleroderma); anti-Jo-1 (antisynthetase syndrome / inflammatory myopathy); anti-U1RNP (mixed connective tissue disease). The clinical pattern and titre guide interpretation.
ANCA (Antineutrophil Cytoplasmic Antibody)
ANCA are associated with systemic vasculitides. Two main patterns are recognised by IIF: cANCA (cytoplasmic pattern, usually directed against PR3/proteinase 3) — associated with granulomatosis with polyangiitis (GPA); and pANCA (perinuclear pattern, usually directed against MPO/myeloperoxidase) — associated with microscopic polyangiitis (MPA) and eosinophilic GPA (EGPA). ANCA results should be confirmed by PR3-ANCA and MPO-ANCA ELISA.
Rheumatoid Factor and Anti-CCP
Rheumatoid factor (RF) is an IgM antibody directed against the Fc portion of IgG. It is elevated in ~70–80% of rheumatoid arthritis (RA) patients but also in Sjögren’s, SLE, cryoglobulinaemia, and various infections, limiting its specificity. Anti-cyclic citrullinated peptide (anti-CCP) antibodies have similar sensitivity (~70%) to RF but much higher specificity (>95%) for RA. Anti-CCP can precede clinical disease by years and is used in the 2010 ACR/EULAR RA classification criteria.
References
- Aringer M, et al. 2019 European League Against Rheumatism/American College of Rheumatology Classification Criteria for Systemic Lupus Erythematosus. Arthritis Rheumatol. 2019.
- Bossuyt X, et al. Position paper: recommendations for the laboratory detection of autoantibodies. Clin Chem Lab Med. 2017.
- NHS. Antinuclear antibody test. nhs.uk