Immunoglobulin G (IgG) antibodies are produced by the lymphocytes in the
synovial membranes. They act as antigens. Other IgG and IgM antibodies
react with these abnormal antigens to produce immune complexes. The
reactive IgM is called the Rheumatoid Factor (RF).
In English that means
that in people with RA the immune system goes haywire and the process
creates some abnormal antibodies.
The RF is a
measurement of the reactive IgM antibodies. It is important to note that
the exact role of these antibodies in rheumatoid arthritis is not yet
Approximately 80% of
the people with rheumatoid arthritis have positive titers. The other 20%
are considered seronegative which means the have no identifiable RF
present. So, a negative RF
does not rule out the existence of RA. The factor may also be found in
the presence of other autoimmune diseases and even in a small percentage
of healthy people.
Type of Test:
What the Results
The Rheumatoid Factor
is usually expressed as titer.
A normal or negative
titer is less than 1:20.
Levels between 1:20
and 1:80 may indicate something is going on, but not necessarily
rheumatoid arthritis. Other autoimmune diseases such as lupus and
Sjogrens syndrome may cause a low positive titer. Heart disease,
liver disease, mononucleosis and other conditions may also cause a
Titers over 1:80 are
usually, but not always indicative of rheumatoid arthritis.
Since this is not a
definitive test, a diagnosis should never be based solely on the results
of the rheumatoid factor.
Common Blood Tests : What Every Patient Must Know About Lab Tests by N.
Mosby's Manual of Diagnostic and Laboratory Tests by
Kathleen Deska Pagana, Timothy James Pagana.