From the Guidelines
Laboratory tests for rheumatoid arthritis (RA) should include rheumatoid factor (RF), anti-cyclic citrullinated peptide (anti-CCP) antibodies, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) to diagnose and monitor the condition. These tests are essential in assessing inflammation levels and disease activity, and should be interpreted together with clinical symptoms, as no single test can definitively diagnose RA 1.
Key Laboratory Tests
- Rheumatoid factor (RF) and anti-CCP antibodies are present in about 70-80% of RA patients, with anti-CCP being highly specific and can appear years before symptoms develop
- Inflammatory markers like ESR and CRP are used to assess inflammation levels and disease activity
- Complete blood count (CBC) may show anemia of chronic disease, which is common in RA
- Comprehensive metabolic panel helps evaluate organ function and monitor medication side effects
- Synovial fluid analysis from affected joints can rule out other conditions like gout or infection
Imaging Tests
- Imaging tests like X-rays, ultrasound, and MRI complement laboratory tests by showing joint damage
- These tests should be used to monitor disease progression and treatment effectiveness, allowing for timely adjustments to therapy
Monitoring and Follow-up
- Regular monitoring of disease activity and laboratory tests is crucial in managing RA, with follow-up intervals depending on the therapeutic agents used and the patient's response to treatment 1
- The 2015 American College of Rheumatology guideline for the treatment of rheumatoid arthritis provides recommendations for optimal follow-up laboratory monitoring intervals for patients with RA receiving disease-modifying antirheumatic drugs (DMARDs) 1
From the Research
Lab Tests for Rheumatoid Arthritis
The following lab tests are used to diagnose rheumatoid arthritis:
- Rheumatoid factor (RF) 2, 3, 4, 5
- Anti-citrullinated protein antibody (anti-CCP) 2, 3, 4, 5
- C-reactive protein (CRP) 2, 3, 5
- Erythrocyte sedimentation rate (ESR) 2, 3, 4, 5
- Complete blood count with differential 2
- Assessment of renal and hepatic function 2
Diagnostic Criteria
The diagnosis of rheumatoid arthritis is based on the presence of at least one joint with definite swelling that is not explained by another disease 2, 6. The likelihood of a rheumatoid arthritis diagnosis increases with the number of small joints involved 2.
Test Sensitivity and Specificity
The sensitivity and specificity of the lab tests for rheumatoid arthritis are:
- RF: 91.0% sensitivity, 74.4% specificity 3
- Anti-CCP: 88.0% sensitivity, 90.4% specificity 3
- Combination of RF and anti-CCP: 90.2% sensitivity, 83.3% specificity 3
Prognostic Value
The presence of both RF and anti-CCP antibodies is associated with a worse outcome in rheumatoid arthritis patients, including lower remission rates and higher baseline ESR 4. The diagnostic utility of anti-CCP antibodies is higher than other markers, including RF, CRP, and ESR, in patients with erosive rheumatoid arthritis 5.