The diagnosis of rheumatoid arthritis

Rheumatoid arthritis is fairly easy to diagnose. At the outset, the doctor will seek to rule out a number of other disorders which share some of the same symptoms. The best known are osteoarthritis, gout and some forms of joint infection. These can be eliminated with considerable certainty by applying the criteria of the American Rheumatism Association, which combine clinical examination, blood tests and X-ray evidence.

The medical criteria establishing whether a person has RA will be determined during careful questioning and an examination. Blood tests are useful in confirming the existence of chronic inflammation. Many people with RA will be anaemic (they will have a reduced amount of iron in their blood) and have increased numbers of the blood platelets which are involved in the clotting process. Their red blood cells may also settle faster that those of someone who does not have the disease. They may also have raised levels of particular blood proteins that are indicators of disease activity or immune stimulation. Rheumatoid factor will also be measured, as it is present in significant amounts in 70 to 85 per cent of people with RA at the onset of the disease.

Tests may also be carried out for some other less common blood proteins which may confirm the diagnosis. An X-ray of the hands may be taken, as bone-thinning around the joints occurs early. Erosions of bone are not usually visible for several months after the onset of the disease, except through the use of specialised techniques such as microfocal X-ray. When all these criteria are taken together, the doctor will be at least 90 per cent certain that the diagnosis is correct.