Blood Test for Rheumatoid Arthritis II
One important step in dealing with the affects of rheumatoid
arthritis, also known as “RA”, is arriving at the diagnosis. While a
person’s clinical signs and symptoms often point toward RA,
confirmation by certain tests is usually necessary. Some of the same
tests are also used later to assess whether the disease is active or
in remission as well as determining how effective therapy is in
controlling the disease.
X-rays and other imaging studies are done to determine if damage to
joints has already occurred, and if so, to what extent. Since lung
problems are often associated with RA, a chest x-ray is also often
done as well. But much of the testing for RA involves drawing blood
for laboratory testing, and understanding what each test is about
helps in understanding how a patient is doing. No one test is enough
to diagnose or rule out rheumatoid arthritis.
One blood test that is commonly done is the CBC or complete blood
count. This determines the number of red blood cells or erythrocytes
to rule out anemia, which is a common complication in RA. A WBC or
white blood count of leukocytes is done to gauge both inflammation
and the possibility of a bacterial infection coexisting with the RA.
The type and percentage of white cells present also gives valuable
information. Finally, a platelet count helps in determining the
ability of the blood to clot in injuries. Some of the common drugs
used to treat RA can affect the blood count, so this test may be
done throughout the course of the illness.
Another test is for the rheumatic factor, or RF, and is often
referred to as a “latex test” from the way it is done in the lab.
Levels of RF are associated with increased autoimmune activity and
used both to diagnose the condition and to see how well medications
are working, but about 20% of RA patients do not have a positive RF
test. They still can clearly have RA and are referred to as “seronegative.”
There are also many people who have a positive RF test but who do
not have RA and are perfectly healthy.
Blood is also often tested for C-reactive protein, or CRP. This
blood test assesses the presence or absence of inflammation in the
body and is also used both for diagnosis and for assessment of
treatment effectiveness. Another test used the same way is the ESR
or “sed rate.” This test determines how fast red blood cells settle
in a special test column and the faster they fall, the more
inflammation is present. This test is elevated for about 60% of RA
patients but is not specific for it.
ANA or anti-nuclear antibody testing may also be done. Roughly 30%
to 40% have these antibodies against the self and will test
positive, but this test is also positive in other diseases such as
lupus. If an RA patient does have these auto-antibodies, checking
their levels can be used to see how well therapy is doing. Not all
doctors will test for all of these things as each patient and their
case of RA are unique and must be treated individually. Hopefully
most patients will feel free to ask questions about any tests they
do not understand or do not feel they might need. This holds true
for all tests ordered for you since your doctor should be your
partner in care.
Resources
List of RA blood tests and why they are done:
www.webmd.com/rheumatoid-arthritis/guide/blood-tests
Laboratory testing in the diagnosis of RA:
www.orthop.washington.edu/
Use of blood tests to determine condition during treatment of RA:
healthlink.mcw.edu/article/
Discusses the latex test for the rheumatoid factor (RF):
www.arthritis-pain-cure.com/
Very complete information on the Arthritis Foundation website about
testing for diagnosis and treatment of RA:
www.arthritis.org/