Rheumatoid Arthritis Diagnostics

Laboratory Tests and Ancillaries

Rheumatoid factor is present in approximately 60-80% of patients with rheumatoid arthritis. Rheumatoid factor titers rarely change with disease activity, hence it is not recommended in monitoring patients with rheumatoid arthritis but it is useful in its diagnosis especially if measured with the anti-citrullinated protein antibody. 

Anti-citrullinated Protein Antibody (ACPA) shows similar diagnostic sensitivity as rheumatoid factor but with a higher specificity rate of approximately 95-98%. It is likewise not recommended in monitoring patients with rheumatoid arthritis. 

The presence of both rheumatoid factor and anti-citrullinated protein antibody show a more severe disease.

Other important laboratory examinations for rheumatoid arthritis include acute-phase reactants and complete blood count. The inflammatory markers erythrocyte sedimentation rate and C-reactive protein are not specific for rheumatoid arthritis, but they reflect the degree of synovial inflammation.  Monitoring of these acute-phase reactants can be used to assess disease activity. A complete blood count may show anemia of chronic disease, leukocytosis, and thrombocytosis.

Imaging

X-ray is commonly used to assess the presence of joint damage secondary to rheumatoid arthritis although it may have decreased sensitivity if taken during the first six months of the course of the disease. Early changes seen in an X-ray include soft-tissue swelling and juxta-articular demineralization while later changes involve erosions through the cortex of the bone and around the margins of the joint. Flexion and extension views of the cervical spine on plain X-ray may be used to detect atlanto-axial subluxation which can suggest cervical myelopathy.

Magnetic resonance imaging (MRI) is more sensitive than standard radiography for detecting bone destruction. It detects bone erosions and subclinical synovitis earlier in the course of the disease. It may be used in patients with suggestive cervical myelopathy.

Ultrasonography is an alternative method to estimate the degree of inflammation and volume of inflamed tissue, although it should not be used for routine disease activity monitoring in adults with rheumatoid arthritis. As with MRI, it shows features of joint inflammation that are not physically evident (eg subclinical synovitis for suspected rheumatoid arthritis) and detects bone erosions in early disease. It may also be used to assess the joints for intra-articular steroid injections.