Blood Tests for Rheumatoid Arthritis

Introduction

Rheumatoid arthritis is an autoimmune, inflammatory disorder characterized by symmetrical, widespread joint involvement. Although the most pronounced signs and symptoms of rheumatoid arthritis (RA) are joint swelling and joint pains, it is a systemic (the whole body is affected) disorder which can involve other body systems such as the heart, skin, and eyes. The term “autoimmune” signifies that the body’s own immune mechanisms recognize the body’s cells as “foreign” or “non-self” and attacks them.

Rheumatoid arthritis affects approximately 1% of the general population, and results in more than 250,000 hospitalizations per year. Women are twice as likely to suffer from the disease than men, and if left untreated it can cause severe deformities and disabilities.

Blood Tests for RA

The diagnosis of rheumatoid arthritis is often complex and does not rely on any one physical examination finding or laboratory result alone. It is mainly diagnosed clinically, which means that the diagnosis is largely based on clinical signs and symptoms and not one laboratory test is specific for the disease.

One of the most commonly used blood tests for rheumatoid arthritis is the rheumatoid factor (RF), which are basically antibodies directed against the body’s own cells. However, RF is not a specific test for rheumatoid arthritis, meaning a positive test result will not guarantee a diagnosis of RA. Many other diseases will cause yield a positive result of this test, which include Sjogren’s syndrome (another form of autoimmune disease), subacute bacterial endocarditis, malaria, syphilis, and tuberculosis, among others.

Studies indicate that the value of rheumatoid factor lies in its usefulness in monitoring disease progression or response to treatment. Lowered levels of this blood test after a particular therapy indicates that the treatment is effective. Increasing levels of RF may indicate that the disease is progressing or worsening. Patients with high levels of RF are more likely to have more severe disease and involvement of other body systems than those with low levels.

Other Tests

There are other blood tests which are done in cases where a diagnosis of rheumatoid arthritis is suspected. These are:

• Erythrocyte sedimentation rate (ESR) - an elevated value for this test indicates that there is an ongoing inflammatory process in the body. However, this test is also not specific for rheumatoid arthritis.
• C-reactive protein (CRP) - this test is also used to determine whether an active inflammatory process is present in the body, and again is not a specific test for RA.

Diagnosis

Rheumatoid arthritis is not diagnosed through laboratory test. Rather, its diagnosis depends on the presence of several diagnostic criteria, as recommended by the American Rheumatism Association. These include:

• stiffness of affected joints upon awakening (morning stiffness)
• arthritis of three or more joints
• involvement of hand joints
• symmetric joint involvement
• presence of rheumatoid nodules
• rheumatoid factor positive
• x-ray findings of affected joints

References

American College of Rheumatology Guidelines for the Management of Rheumatoid Arthritis

American Academy of Family Physicians: Diagnosis and Management of Rheumatoid Arthritis

American Rheumatism Association Diagnostic Criteria for Rheumatoid Arthritis