Blood Test for Rheumatoid Arthritis
The initial diagnosis of rheumatoid arthritis (RA) is often made
from the history of the patient, but confirmation comes with a
series of tests. These may include x-rays, MRIs, cat scans and other
imaging, but will always include some blood tests. While no one
likes needles, it is an important part of both making a diagnosis
and also in monitoring how active the disease may be after
diagnosis. Other blood tests in addition to those mentioned here may
be done based on the individual clinical case.
The first test is usually the very common CBC or complete blood count, along with a differential cell count and platelet count. There are several reasons for this testing. One is that people with RA frequently are anemic and have abnormal or deficient red blood cells. These cells, also called erythrocytes, carry oxygen to every tissue in the body as well as carrying off waste carbon dioxide to the lungs. Thus they are critically important to life and health. If anemia is present, it will need to be treated. Platelets are the cells that help the blood to clot in injury and some cases of RA and other arthritis related diseases have abnormal platelet counts and function. Test on clotting ability and such tests as FSP, PT and PTT may also be ordered.
White blood cells or leukocytes are important to fight infection and active in inflammation. They may be abnormally high or low in RA, and can also indicate the presence of infections. Since DMARDs, steroids, and biologic modifiers all suppress the normal immune system function as well as the abnormal autoimmune reaction, screening for infections can be important after diagnosis as well.
Another test commonly done is called a latex test or rheumatoid factor (RF) test. About 70% to 80% of people with RA are what is called seropositive and will test positive for RF, while another 20% to 30% will not have detectable RF and are called seronegative. For those who do have the RF, the higher the number of the test, the more active the disease is in the body, so the test for RF is used to both diagnose the condition and to monitor effectiveness of treatment.
Another test is called a “sed rate” or ESR which stands for erythrocyte sedimentation rate. It is a rough estimate of how much inflammation is in the body and usually is noticeably elevated in patients with RA and certain other diseases. It is normally somewhat higher in women than in men.
Blood may also be tested for CRP or C-reactive protein. This is also a general indication of the presence of inflammation and is not specific for RA alone. While the sed rate or ESR is done for the same purpose, sometimes the CRP will be elevated when the ESR is not, and vice versa, so both tests may be done both to monitor inflammation as well as to diagnose RA.
Another test that is sometimes done is the ANA or antinuclear antibody test. This test measures antibodies that have formed against normal body cells and about 30% to 40% of RA patients will test positive for ANA. However, some people will have positive ANA tests and not have any illness at all, so it is not a specific test for RA.
Some other tests such as complements and other tests may also be done to piece together the diagnosis of RA, but the clinical picture is also taken into consideration. Occasionally a patient may have few or no positive blood tests but have the obvious symptoms of RA, but usually test results are helpful in making the diagnosis. During treatment, the test will be done to see if the disease is active or in remission, and how high disease activity may be.
General information about laboratory tests for rheumatoid arthritis:
Lab test information and tips for living with RA:
More about blood tests for RA:
Arthritis Foundation information on the diagnosis of RA with blood tests:
Very complete discussion of RA blood tests and what they mean: