| 🔬 Autoantibody | 🩺 Disease / Notes | 📊 Diagnostic Levels |
|---|
| 🧪 Rheumatoid Factor (RF) |
Antibodies against Fc fragment of IgG (IgM, IgG, IgA – usually measure IgM).
• ~75% RA; 100% if extra-articular disease.
• 5% healthy population.
• Also in SLE, Sjögren’s, systemic sclerosis, cryoglobulinaemia, hepatitis C, sarcoidosis, malignancy.
|
Positive if >20 IU/mL.
High titres (>60 IU/mL) = severe, extra-articular RA risk.
|
| 🎯 Anti-cyclic citrullinated peptide (ACPA / anti-CCP) |
• ~70% RA.
• Much more specific than RF.
• Can precede diagnosis by years.
• Suggests erosive/severe RA.
|
Significant if >20 U/mL (lab-dependent).
High titres (>60 U/mL) strongly predictive of erosive RA.
|
| 🌙 Antinuclear Antibodies (ANA) |
Non-specific autoimmunity marker.
• SLE, Sjögren’s, systemic sclerosis, infections, sometimes normal.
• Pattern (homogeneous, speckled, nucleolar, centromere) gives clues.
|
Positive if titre ≥1:80 (HEp-2).
High titres (≥1:320) more likely pathological.
|
| 🧬 Anti-topoisomerase I (Scl-70) |
Diffuse cutaneous systemic sclerosis (dcSSc). |
Detected by ELISA / immunoblot; no strict cut-off but strong positivity is highly specific. |
| 💪 Anti-Jo-1 |
Polymyositis, dermatomyositis (esp. with ILD). |
Positive if >20 U/mL (lab-dependent). Often high titres in active disease. |
| 🎯 Anti-centromere |
Limited cutaneous systemic sclerosis (lcSSc, CREST). |
ANA pattern: centromeric dots at titres ≥1:160 = diagnostic. |
| 📝 Anti-RNA polymerase I & III |
Systemic sclerosis (renal crisis, diffuse cutaneous disease). |
Qualitative (present/absent); high specificity. |
| 🔥 c-ANCA (anti-PR3) |
Granulomatosis with polyangiitis (Wegener’s). |
Positive if >20 U/mL. High titres correlate with active vasculitis. |
| 💡 p-ANCA (anti-MPO) |
Microscopic polyangiitis, EGPA (Churg–Strauss). |
Positive if >20 U/mL. Rising titres may suggest relapse. |
| 🧫 Anti-dsDNA (IgG) |
SLE (specific, correlates with activity, especially lupus nephritis).
|
Positive if >30 IU/mL.
High titres (>100 IU/mL) = strong correlation with lupus nephritis.
|
| 💊 Anti-histone |
Drug-induced lupus (e.g. hydralazine, procainamide, isoniazid). |
Usually very high titres in drug-induced lupus; low titres in SLE. |
| 🌞 Anti-Ro (SS-A) |
Sjögren’s, SLE; neonatal lupus & congenital heart block risk. |
Positive if >10 U/mL. High titres increase neonatal lupus risk. |
| 🌙 Anti-La (SS-B) |
Sjögren’s, SLE. |
Positive if >10 U/mL (usually co-exists with Anti-Ro). |
| 🩸 Anti-β2 glycoprotein I |
Antiphospholipid syndrome (thrombosis, pregnancy morbidity). |
Medium/high titre = >40 GPL/MPL or >99th percentile, on ≥2 occasions ≥12 weeks apart.
Low transient titres often post-infection.
|
