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.
Resources
General information about laboratory tests for rheumatoid arthritis:
www.webmd.com/rheumatoid-arthritis/guide/blood-tests
Lab test information and tips for living with RA:
www.orthop.washington.edu/
More about blood tests for RA:
www.healthlink.mcw.edu/article/924811109.html
www.arthritis-pain-cure.com/
Arthritis Foundation information on the diagnosis of RA with blood
tests:
http://www.arthritis.org/
Very complete discussion of RA blood tests and what they mean:
http://arthritis.about.com/