What are the diagnostic criteria for rheumatoid arthritis (RA)?

Diagnostic Criteria for Rheumatoid Arthritis

The diagnosis of rheumatoid arthritis requires definite clinical synovitis in at least one joint not better explained by another disease, with a score of ≥6/10 points based on the 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria. 1

ACR/EULAR 2010 Classification Criteria

Joint Involvement (0-5 points)

• 1 large joint = 0 points 1
• 2-10 large joints = 1 point 1
• 1-3 small joints = 2 points 1
• 4-10 small joints = 3 points 1

• 10 joints (at least 1 small joint) = 5 points 1

Serology (0-3 points)

• Negative RF and negative ACPA = 0 points 1, 2
• Low positive RF or low positive ACPA = 2 points 1, 2
• High positive RF or high positive ACPA = 3 points 1, 2

Acute Phase Reactants (0-1 points)

• Normal CRP and normal ESR = 0 points 1
• Abnormal CRP or abnormal ESR = 1 point 1

Duration of Symptoms (0-1 points)

• <6 weeks = 0 points 1
• ≥6 weeks = 1 point 1

Clinical Features

Characteristic Joint Involvement

• Symmetric polyarticular involvement is typical 1, 3
• Most commonly affects metacarpophalangeal joints, proximal interphalangeal joints, wrists, and metatarsophalangeal joints 1, 3, 4
• Large joints (shoulders, elbows, hips, knees, ankles) may also be involved 1, 3
• Distal interphalangeal joints, first carpometacarpal joints, and first metatarsophalangeal joints are typically spared 1
• Morning stiffness lasting at least 1 hour is characteristic 3, 5

Laboratory Assessment

Essential Tests

• Rheumatoid factor (RF) - present in approximately 80% of patients 4, 5
• Anti-citrullinated protein antibody (ACPA) - highly specific for RA 1, 5
• Acute phase reactants: C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) 1, 5
• Complete blood count with differential 5
• Renal and hepatic function tests 5

Imaging

Radiography

• Initial imaging method for detecting damage 1
• Characteristic findings include periarticular osteopenia, uniform joint space narrowing, and osseous erosions 1
• May be normal in early disease 3

Advanced Imaging

• Ultrasound can detect synovitis and is superior to clinical examination for detecting inflammation 1
• MRI is more sensitive than ultrasound in early RA and can detect bone marrow edema and synovitis, which predict disease progression 1
• Advanced imaging is particularly valuable when clinical findings are equivocal but suspicion remains high 1, 2

Diagnostic Algorithm

1. Identify clinical synovitis in at least one joint not explained by another condition 1, 5, 6
2. Apply the 2010 ACR/EULAR criteria scoring system 1
3. If score ≥6/10, diagnose as definite RA 1
4. If score <6/10 but clinical suspicion remains high, consider:
   • Advanced imaging (ultrasound or MRI) to detect subclinical synovitis 1, 2
   • Repeat serological testing as seroconversion can occur over time 2
   • Follow-up evaluation as patients may develop additional features 1

Common Pitfalls and Caveats

• A negative RF does not exclude RA diagnosis - approximately 20% of patients are seronegative 4
• Early RA may present with only one or few joints involved, making diagnosis challenging 1, 6
• Alternative diagnoses to consider when RA is suspected include psoriatic arthritis, crystal arthropathies (gout, pseudogout), other inflammatory arthritides, and osteoarthritis 2
• The presence of extra-articular manifestations (rheumatoid nodules, vasculitis) typically occurs in established disease and supports the diagnosis 3, 4
• Treatment should not be delayed while awaiting definitive classification, as early intervention improves outcomes 6