Diagnostic
Tests For Rheumatoid Arthritis In order to help simplify the diagnostic
process of RA, the American College of Rheumatism has developed criteria, where
4 or more factors are required to be positive in order to make the diagnosis of
rheumatoid arthritis (RA). Below is a table listing these criteria (modified
from Ref. 2, p. 418). Other blood tests often show a moderate, but non specific
anemia. The ESR (sedimentaion rate of the red blood cells) is often elevated significantly
as is the rheumatoid factor (=RF). If the RF is tested with the Latex fixation
tests, a value of 1:160 dilution titer or more is indicative of possible RA. The
higher the value, the worse the longterm outcome. When anti-inflammatory treatment
modalities control the synovitis in the affected joints, often the RF titer goes
down to lower levels. Another useful blood test is the C-reactive protein (CRP),
which is positive when the RA is in an active phase. Similar to the RF titer
the CRP test is a predictor of how progressive the RA is at the particular time
when the test was taken. In other words, if the anti-inflammatory therapy is clinically
successful, then usually the CRP test improves.
| Diagnostic
criteria for rheumatoid arthritis (RA) |
| 4 of these criteria must be present
to make the diagnosis of RA: |
- morning stiffness lasts longer than 1 hour
- arthritis
of hand joints (MCP joints or IP joints) or wrist
- arthritis
of 3 or more joints
- rheumatoid nodules
- the
arthritis presents in symmetrical fashion
- positive RF
( less than 5% of normals have a false negative RF)
- X-ray
changes showing erosions or bony decalcification
|
Liver function tests often show the transaminases and the
alkaline phosphatase to be moderately elevated when RA is active( Ref. 1). Erosions,
which are typical for RA, take about three years to show on X-rays. These develop
in about 90% or more of patients with RA. Other signs on the X-ray films are a
localized form of osteoporosis just around the affected joints (periarticular
osteoporosis), loss of joint space and swelling of the soft tissues (Ref.1). Differential
diagnosis: There are a number of similar rheumatic illnesses that
can present in a similar fashion with joint pains and swelling. Lupus erythematosusaffects
joints, but can also affect the cardiovascular system and interal organs more
due to the anti nuclear antibodies (a positive ANA blood test shows this).Polymyalgia
rheumatica can be undistinguishable from RA in elderly patients.
Palindromic
rheumatism mimics degenerative arthritis by affecting only one or
very view major joints. However, about 50% of these patients will develop
typical RA later in life, in other words the initial symptoms were only atypical
for RA. When the clinical picture develops into the typical RA pattern, the RF
at that point in time usually also turns positive (Ref. 1). Other less
common illnesses such as sarcoidosis, psoriatic arthritis, gonococcal
arthritis and Reiter's syndromecan all mimic RA. Finally, gout, pseudogout and
osteoarthritis (degenerative arthritis) can also be mistaken for RA. However,
details of clinical presentation, X-rays and blood tests will help to delineate
these from RA.
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