Autoimmune blood tests and what they detect
| Test | Primary disease | Sensitivity |
|---|---|---|
| ANA (antinuclear antibody) | Lupus (SLE) — screening test | 95% in SLE |
| Anti-dsDNA | Lupus — specific, tracks disease activity | 70% in SLE |
| Anti-Sm | Lupus — highly specific | 25% in SLE |
| Anti-Ro (SSA) / Anti-La (SSB) | Sjögren's syndrome, neonatal lupus | ~75% in Sjögren's |
| Rheumatoid Factor (RF) | Rheumatoid arthritis (RA) | 70–80% in RA |
| Anti-CCP | Rheumatoid arthritis — more specific than RF | 70–80% in RA, >99% specific |
| Anti-Scl-70 (anti-topoisomerase) | Diffuse cutaneous scleroderma | ~40% in scleroderma |
| Anti-centromere | Limited scleroderma (CREST syndrome) | ~80% in limited scleroderma |
| ANCA (PR3 / MPO) | Vasculitis (GPA, MPA) | ~90% in active GPA |
| Anti-Jo-1 | Polymyositis / dermatomyositis | ~25% in IIM |
| Complement C3 & C4 | Low in lupus flares, hereditary complement deficiency | Track disease activity |
ANA — the starting point
Why ANA is ordered first
ANA is ordered as the first screening test when an autoimmune condition is suspected. A positive ANA at titre ≥1:80 prompts further specific antibody tests to identify the exact disease. A negative ANA makes most ANA-associated diseases (lupus, Sjögren's, scleroderma) very unlikely. However, some autoimmune diseases are ANA-negative — notably RA, ANCA vasculitis, and anti-Jo-1 myositis.
Complement levels in autoimmune disease
Complement proteins (C3 and C4) are part of the immune system. In lupus, immune complexes consume complement, causing low C3 and C4 — especially during flares. Low complement with high anti-dsDNA is a reliable indicator of lupus disease activity and kidney involvement. Complement is normal or raised in RA and most other autoimmune conditions.
Questions to ask your rheumatologist
- Which specific antibodies are positive in my case?
- Do my antibody patterns point to one diagnosis?
- Is my complement low — indicating active lupus?
- Do I need further organ-specific investigations (kidney biopsy, lung function)?
Medical Disclaimer: For educational purposes only. Always consult a qualified healthcare professional for diagnosis and treatment.