How Is Rheumatoid Arthritis Diagnosed?
In its early stages rheumatoid arthritis may be difficult to diagnose. Its signs and symptoms - especially stiffness and inflammation - are similar to several other conditions.A GP (general practitioner, primary care physician) will carry out a physical examination. The doctor will carefully check the joints to see if there is any swelling (e.g. “pain on squeeze test” on the knuckles), as well as determining how easily they move. The patient will be asked about symptoms. To help the doctor make a correct diagnosis, the National Health Service (NHS), UK, urges patients to tell the doctor about all their symptoms, and not just the ones they consider to be important.
The doctor may also order the following tests:
Blood tests
- Erythrocyte sedimentation rate (ESR or sed rate) - this blood test detects and monitors inflammation in the body by measuring the rate at which red blood cells in a test tube separate from blood serum over a set period, becoming sediment in the bottom of the test tube. A high sedimentation rate is linked to more inflammation. In other words, if the red blood cells sink faster to the bottom of the test tube, it could mean that the patient has an inflammatory condition, such as rheumatoid arthritis.
- C-reactive protein (CRP) - CRP is produced by the liver. A higher CRP level is linked to the presence of inflammation in the body.
- Anemia - a significant proportion of patients with rheumatoid arthritis also have anemia; when not enough oxygen is carried in the blood, because of a lack of red blood cells. If the patient is found to have anemia it does not necessarily mean they have rheumatoid arthritis.
- Rheumatoid factor - this blood test determines whether rheumatoid factor (an antibody) is present in the patient’s blood. The majority of rheumatoid arthritis patients have this abnormal antibody in their bloodstream (according to the National Rheumatoid Arthritis Society, UK, 30% of patients with rheumatoid arthritis do not have rheumatoid factor). During the early stages of the disease it is sometimes difficult to detect rheumatoid factor. As this antibody is present in a small proportion of people without rheumatoid arthritis, this test cannot confirm the disease definitively.
MRI (magnetic resonance imaging) scans - can help the doctor determine more specifically what damage has been done to a joint. An MRI machine uses a magnetic field and radio waves to create detailed images of the body.
Diagnostic criteria
In 1987, the American College of Rheumatology defined the following criteria for the classification of rheumatoid arthritis:- Morning stiffness of more than an hour most mornings for a period of at least six weeks.
- Arthritis and soft-tissue swelling of more than 3 of 14 joints/joint groups, present for a period of at least six weeks.
- Arthritis of hand joints, which are present for a period of at least six weeks.
- Symmetric arthritis, which is present for a period of at least six weeks.
- Subcutaneous nodules in specific places.
- Rheumatoid factor at a level > the 95th percentile.
- Radiological changes suggestive of joint erosion.
Most health care professionals as well as their patients prefer to have the condition treated as early as possible to prevent bone erosion - even if the American College of Rheumatology criteria are not yet met.
The American College of Rheumatology criteria are useful for categorizing established rheumatoid arthritis, especially when studying the causes, distribution, and control of the disease in populations (epidemiology).
Distinguishing rheumatoid arthritis from other medical conditions
At the time of diagnosis rheumatoid arthritis needs to be distinguished from other possible conditions which may have similar signs and symptoms. These include:- Gout and pseudogout (crystal induced arthritis) - this usually involves specific joints. It can be distinguished from rheumatoid arthritis by aspirating joint fluid.
- Osteoarthritis - blood tests and X-rays of the affected joints can help distinguish this condition.
- SLE (systemic lupus erythematosis) - specific clinical symptoms and blood tests (antibodies against double-stranded DNA) can distinguish this condition from rheumatoid arthritis.
- A specific type of psoriatic arthritis - can be distinguished from rheumatoid arthritis by checking nail changes and skin symptoms.
- Lyme disease - can be distinguished from rheumatoid arthritis with blood tests in endemic areas.
- Reactive arthritis (used to be known as Reiter’s disease) - usually linked with urethritis, conjunctivitis, iritis, painless mouth ulcers and keratoderma blennorrhagica. The arthritis is not symmetrical and usually involves the heel, sacroiliac joints, as well as the large joints of the leg. In cases of rheumatoid arthritis joints are symmetrically involved (e.g. both knees, both hands, etc).
- Ankylosing spondylitis - involves the spine and generally affects men. However, several joints may be affected symmetrically, as with rheumatoid arthritis.
- Sarcoidosis
- Amyloidosis
- Whipple’s disease
- Acute rheumatic fever
- Gonococcal arthritis
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