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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.