Rheumatoid arthritis is diagnosed by a combination of a medical history, a physical examination and specialised tests or investigations. If a diagnosis of rheumatoid arthritis is suspected, patients should be referred to a specialist called a rheumatologist.

History
The history of an illness refers to the pattern of symptoms it causes in an individual patient. Symptoms that would lead a doctor to suspect a diagnosis of rheumatoid arthritis include:

• pain, stiffness and swelling affecting several joints on both sides of the body, especially the small joints of the hands, wrists, feet or knees
• morning stiffness that lasts an hour or more
• tiredness, lethargy or flu-like symptoms
• loss of appetite and weight

Examination
A physical examination involves inspecting the joints for signs of rheumatoid arthritis. During an examination, a doctor looks carefully at the joints for any sign of swelling, redness or joint deformities. The doctor will also look for other signs of rheumatoid arthritis, such as rheumatoid nodules or paleness due to anaemia.
A physical examination also involves feeling and moving the joints. In patients with rheumatoid arthritis, affected joints feel hot, swollen and ‘boggy’, are stiff and painful when moved and have a limited range of movement (i.e. cannot bend as far as usual).

Blood tests

A number of blood tests are used to help confirm a diagnosis of rheumatoid arthritis, but there is not any one test that proves the diagnosis.
As rheumatoid arthritis is an autoimmune disease, blood tests that detect abnormal immune function can help to diagnose it. The most important of these is a test for something called rheumatoid factor.

Rheumatoid factor
Rheumatoid factor is an autoantibody – that is, an antibody directed against the body’s own tissues. Rheumatoid factor is detectable in around 80% of people with rheumatoid arthritis, although it may not be present in the early stages of the disease. However, around 5% of healthy people have rheumatoid factor in their blood, and it can also be present in some other diseases, such as glandular fever, hepatitis and leukaemia. This means that it cannot be used to make a definite diagnosis because some people with rheumatoid arthritis do not have rheumatoid factor, and some people with rheumatoid factor do not have rheumatoid arthritis.

Another autoantibody sometimes detectable in rheumatoid arthritis is called anti-CCP (anti-cyclic citrullinated peptide). This may be detected earlier in the course of rheumatoid arthritis than rheumatoid factor. However, like rheumatoid factor, it can only be detected in 70–80% of cases.
Other blood tests that are used to help diagnose rheumatoid arthritis are those that measure the level of inflammation in the body. These are elevated in lots of different inflammatory conditions but can help to confirm that an inflammatory process is going on. They include tests for:

• ESR (erythrocyte sedimentation rate – how quickly red blood cells clump together and sink in a test tube; inflammatory chemicals make this process happen faster)
• plasma viscosity (how thick the blood is, which is increased by the presence of inflammatory proteins)
• CRP (C-reactive protein, an inflammatory protein)

A blood count may also be performed to check for anaemia (a low red blood cell count).

X-rays and scans

In early rheumatoid arthritis, X-rays may look normal. As the disease progresses, X-rays may show signs of:

• bone thinning
• narrowing of the space between the joint
• swelling of the soft tissues (e.g. the synovial membrane, ligaments and muscles)
• cartilage damage
• bone destruction
• joint deformity

These changes usually show up first in the small joints of the hands and feet. Other scans such as ultrasounds and MRI (magnetic resonance imaging) may also be used to detect signs of rheumatoid arthritis.

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