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It is difficult to diagnose rheumatoid arthritis, but it may be tentatively made on the basis of clinical suspicion, even if these criteria are not present.
The diagnosis doesn't need blood tests or X-rays. It's a mistake to discount the diagnosis on the basis of normal investigations. The clinical examination is the most important aspect of assessment of the problem.
There aren't specific tests for rheumatoid arthritis. A positive Rheumatoid Factor is found in less than 85 percent of patients with the disease. These patients are termed "seropositive". The test is negative in many patients, where it's termed seronegative.
Although its presence doesn't establish the diagnosis, high levels of Rheumatoid Factor may predict a more severe and progressive disease, often with non-joint manifestations. In addition, the test may be positive in other conditions and in the elderly. Once shown to be present, there is no value in testing repeatedly. A new antibody test, anti-CCP antibodies, has been shown to be more specific and useful in the diagnosis of early rheumatoid arthritis.
Those with active rheumatoid arthritis often have anaemia. The erythrocyte sedimentation rate (ESR) is increased in many patients with active disease, as is the C-reactive protein (CRP). These markers of inflammation are useful when raised as they can be used to monitor progress.
A physical exam is usually performed to check the joints for swelling, redness and warmth. Muscles and reflex strength is also checked.
X-rays are not always useful early in the disease, revealing mainly swelling of the soft tissues around the joint and fluid in the joint space. However, the early appearance of erosion of bone around the joint margin indicates a more aggressive disease process and should prompt more aggressive treatment.
As the disease progresses, the abnormalities become more obvious, with a narrowing of joint space and damage to joint margins. X-rays are useful to monitor progress as they provide independent information as to the patient's response to particular therapy.
