Autoimmune diseases occur when the immune system attacks the body's own tissues. They encompass over 80 conditions — from rheumatoid arthritis and lupus to thyroid disease and type 1 diabetes. Blood tests for autoimmunity look for the antibodies and markers produced during these immune attacks.
Key autoimmune markers
- ANA (antinuclear antibodies) — a broad screening test; positive in lupus, Sjögren's syndrome, scleroderma and others; also positive in up to 15% of healthy people
- Anti-dsDNA — more specific for lupus (SLE); used to monitor disease activity
- RF (rheumatoid factor) — elevated in rheumatoid arthritis but also in other conditions and in healthy older adults
- Anti-CCP (anti-cyclic citrullinated peptide) — more specific for RA than RF; useful for early diagnosis
- Anti-TPO (thyroid peroxidase antibodies) — elevated in Hashimoto's thyroiditis and Graves' disease
- ANCA (antineutrophil cytoplasmic antibodies) — associated with vasculitis; two types (pANCA, cANCA) indicate different conditions
- Complement levels (C3, C4) — low complement indicates immune complex consumption; seen in active lupus
What a positive result means (and doesn't mean)
A positive autoimmune antibody test is not a diagnosis. Many of these antibodies occur in healthy people, and interpretation requires the full clinical picture — symptoms, examination, other tests and the titre (level) of the antibody. A low-titre positive ANA in an asymptomatic person rarely means anything significant; the same result in someone with joint pain, fatigue and a rash is a very different finding.
These tests are most useful when ordered for specific clinical reasons. Broad 'autoimmune panels' requested without a clinical context frequently generate more anxiety than insight.