Your ankles ache and your fingers are stiff and swollen. Could it be rheumatoid arthritis (RA)? Blood tests may provide a clue.
The diagnosis of arthritis is made largely through a medical history and physical exam; certain lab tests can help your doctor confirm a suspected diagnosis. With osteoarthritis, blood test results are typically normal, but for RA and other forms of arthritis, blood tests can be key to diagnosing and monitoring the disease. Here are some of the more common blood tests and other tests your doctor may order as part of an arthritis workup and what the results of testing may reveal.
Nancy Hardin, age 71, of Dyersburg, Tenn., was diagnosed with rheumatoid arthritis (RA) 11 years ago. A few months after her diagnosis, she quit her teaching job at a local high school because she could barely walk. Then she started taking the biologic drug Remicade and became nearly symptom-free. Nevertheless, she decided that going back to the classroom would wear her out. She did, though, become a volunteer translator for local Spanish-speaking immigrants and a member of the Tennessee Council...
This blood test, which detects antibodies to cyclic citrullinated peptide (anti-CCP), is useful for diagnosing rheumatoid arthritis. The test can be positive years before symptoms of RA develop. Anti-CCP is present in about 60% to 70% of people with rheumatoid arthritis. When used in conjunction with a test for rheumatoid factor, this test's results are very specific for rheumatoid arthritis. If both tests are done, only 10% to 15% of people with RA will have a negative test. A positive anti-CCP can also predict patients who will develop severe disease.
Limitations: 10% to 15% of people with RA will have a negative test.
Rheumatoid Factor (RF)
Rheumatoid factor (RF) is an abnormal antibody that attaches to an immune system protein in the body called immunoglobulin G (IgG), forming a molecule known as an immune complex. The immune complex can trigger different types of inflammation-related processes in the body. This blood test is eventually positive in 70% to 80% of people with rheumatoid arthritis. The results can help confirm a diagnosis if a patient's signs and symptoms are consistent with those of RA. High levels of rheumatoid factor are associated with more severe disease.
Limitations: Because 70% to 80% of people with RA have high levels of rheumatoid factor, that means 20% to 30% do not. Furthermore, RF can be positive with other diseases, including:
In rare instances the blood test is positive in healthy people.
Antinuclear Antibody (ANA) Test
ANAs are abnormal antibodies directed against the nuclei of the body's cells. High ANA levels may help confirm a diagnosis of lupus. They can also, though, suggest the presence of other autoimmune diseases, such as polymyositis, scleroderma, Sjögren's syndrome, mixed connective tissue disease, or rheumatoid arthritis. Blood tests to detect specific subsets of these antibodies can be used to confirm the diagnosis of a particular disease or form of arthritis.
Limitations: Although a positive ANA suggests an autoimmune disease, it doesn't make the diagnosis alone. Also, a small percentage of healthy people have a positive ANA; about 5% of the general population will have a positive ANA.