Tests that Determine if It's Rheumatoid Arthritis—or Not
Your doctor will take a medical history and perform a physical examination similar to the one used to diagnose osteoarthritis. One goal of the medical history and physical examination is to rule out other possible causes for your symptoms.
You may also be asked to rate your general health and pain level on a scale of one to 10. These are called global assessments. Your doctor will make another global assessment based on your comments and the results of your physical exam. Global assessments provide a baseline measure that will be used for future comparisons.
During the physical, the doctor will look for actively inflamed joints and rheumatoid nodules. Part of the examination is a count of the tender and swollen joints. This count provides an objective measure of your baseline level of disease activity, which the doctor can use to evaluate changes in your condition over time.
The doctor also will check for mechanical joint problems, such as loss of motion, noisy joints, instability, poor alignment and deformities.
You will need to undergo an array of laboratory tests to help the doctor diagnose your disease and provide baseline values that can be used to evaluate disease progression as well as the success of treatment.
The most important laboratory test used in the diagnosis of rheumatoid arthritis is a blood test for rheumatoid factor, an immune substance that is elevated in about 80 percent of people who have the disease. Many people with rheumatoid arthritis initially show no evidence of rheumatoid factor but test positive six to 12 months later, as the disease progresses.
This test alone is not a definitive indicator of rheumatoid arthritis because elevated levels may also occur in people with other autoimmune diseases and with many other unrelated disorders.
Antinuclear antibodies (ANA) are an immune factor found in 30 to 40 percent of people with rheumatoid arthritis. As is the case with rheumatoid factor, ANA may be present in people who do not have rheumatoid arthritis.
Some doctors use a newer, more definitive test to check for rheumatoid arthritis. The test detects antibodies to cyclic citrullinated peptides (CCPs), signs of an immune reaction to the degradation of a protein in the synovium. These antibodies are very specific to rheumatoid arthritis and often appear in the blood long before the onset of rheumatoid arthritis symptoms. Research suggests that this test may be most accurate within three months of the onset of symptoms.
The erythrocyte sedimentation rate, also known as the sed rate, helps differentiate rheumatoid arthritis from osteoarthritis. In rheumatoid arthritis, the inflammation causes red blood cells to clump together and quickly fall to the bottom of a test tube. The sed rate measures the speed at which this occurs. The sed rate is elevated in people with rheumatoid arthritis, but is normal in those with osteoarthritis.
Your doctor may also test you for C-reactive protein (CRP). This substance increases during periods of inflammation.
Your doctor will order a complete blood count (CBC) to measure levels of red blood cells, white blood cells and platelets. People with rheumatoid arthritis often have a low level of oxygen-carrying red blood cells (anemia) and a high level of white blood cells—infection-fighting cells that cause inflammation. Inflammation is also associated with an increased level of platelets—the cells that help the blood to clot.
Other lab tests
Tests may be needed to determine baseline values and check for abnormal function of the liver, kidneys and other organs. These tests may measure electrolytes (minerals that regulate body functions), creatinine (an indicator of kidney function), liver enzymes and blood in the stool. Many drugs used to treat rheumatoid arthritis can be toxic to the liver and kidneys. If, after treatment begins, these tests indicate liver or kidney function abnormalities, your doctor will prescribe other drugs.
You may have a small amount of synovial fluid withdrawn from one of your inflamed joints. The number of white blood cells in the fluid is another helpful measure of inflammation. However, because white blood cells also fight infection, high levels in the synovial fluid may also indicate the presence of infection or another type of disease.
Early in rheumatoid arthritis, joints in the hands and feet often show structural damage on an X-ray. Baseline X-rays provide a starting point against which to measure disease progression.
Bone mineral density test
Your physician may also order a bone mineral density test (BMD). This is an X-ray procedure that uses very low doses of radiation to detect osteoporosis (bone thinning).