In order to help simplify the diagnostic tests for rheumatoid arthritis, 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 (sedimentation 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).
There are a number of similar rheumatic illnesses that can present in a similar fashion with joint pains and swelling. Lupus erythematosus affects joints, but can also affect the cardiovascular system and internal 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 syndrome can 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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