Rheumatoid arthritis (RA) is the chronic inflammation of your joints. The condition affects around 1.3 million adults in the United States, according to the American College of Rheumatology. RA resembles a number of other disorders and conditions. That’s why it often takes time to diagnose.
If you have morning stiffness and pain in symmetrical joints, you and your doctor have some detective work to do. You could have:
Or, simply, you may have a bad mattress.
Blood tests don’t provide a simple yes-or-no answer to whether you have RA. But they can help your doctor steer toward a diagnosis. Blood tests narrow down options and suggest how your disease might progress.
After you receive a diagnosis of RA, continued blood tests will monitor the side effects of drugs used in treatment. They can also help track the progression of the disorder.
Once you leave a sample of your blood at the lab, it may be checked for these factors:
- Rheumatoid factor (RF): RF antibodies collect in the synovium, or tissue lining of your joints. They are present in the blood of many people with RA.
- Erythrocyte sedimentation rate (ESR): A high erythrocyte sedimentation rate may indicate inflammation in your joints.
- C-reactive protein (CRP): This protein may also indicate inflammation in your joints.
- Complete blood count (CBC): This includes hemoglobin and hematocrit tests, which may reveal anemia. This may also be associated with RA.
Rheumatoid factor antibodies gather in the synovium of the joints. The antibodies can also show up if you have another disorder. The most common form of the antibody is called immunoglobulin IgM. When this antibody attaches to healthy body tissue, it can create damage.
The RF test is not perfect for determining if you have RA. While many people with RA display this factor, some don’t. Also, some people who don’t have the condition test positive for RF due to other diseases or disorders, such as:
The results of your RF test will be reported as units per milliliter (u/mL) or the concentration of the antibodies in your blood. Normal levels of RF antibodies in your blood are less than 40 to 60 u/mL, or a concentration under 1:80. Higher numbers indicate a positive RF result.
The higher the figure, the more likely you have RA. But it could also be an indication of Sjogren syndrome. That’s an autoimmune disorder that causes dry eyes and a dry mouth.
The ESR test, is also called a sed rate. It measures inflammation by seeing how red blood cells clump together. In this test, your blood is put into a test tube to observe how quickly erythrocytes — red blood cells — float to the bottom.
The proteins that indicate inflammation cause the red blood cells to stick together and tumble to the bottom of the tube. A faster sedimentation rate indicates greater inflammation.
This ring-shaped protein is produced by the liver as a result of inflammation. CRP doesn’t confirm RA. It reveals the severity of a condition rather than what specifically is wrong. The CRP test may be more sensitive than the ESR test.
If you have a false negative on the RF test, the ESR or CRP test may provide an indication of rheumatoid arthritis.
However, any autoimmune response or bacterial infection may elevate CRP levels, as well. This can complicate the interpretation of the test results.
Complete blood count
Complete blood count is a routine test. It looks at your counts of white and red blood cells. The hematocrit test measures the volume of red blood cells. The hemoglobin test determines your body’s ability to carry oxygen.
Low hemoglobin and hematocrit results (anemia) can be associated with rheumatoid arthritis.
Putting it together
Your healthcare providers will study your blood test results. If you have a combination of RF antibodies and symmetric joint pain, this may suggest RA. Joint pain is most typically found in the:
X-rays showing joint damage can help confirm a diagnosis. Your doctor may also periodically request X-rays to monitor the progress of your disorder.