Test Overview
A rheumatoid factor (RF) blood test
measures the amount of the RF
present in the blood. Normally, antibodies
are produced by the
to help destroy and eliminate invading
bacteria and viruses that can cause disease. But the RF antibody can attach to
normal body tissue, resulting in damage.
A high level of
rheumatoid factor can be caused by several
(including
) and some infections.
Occasionally an elevated level of RF is present in healthy people.
The amount of rheumatoid factor in blood can be measured in two
ways:
- Agglutination tests. One test method mixes blood
with tiny rubber (latex) beads that are covered with human antibodies. If RF is
present, the latex beads clump together (agglutinate). This method is best used
as a first-time screening test for rheumatoid arthritis. Another agglutination
test mixes the blood being tested with a sheep's red blood cells that have been
covered with rabbit antibodies. If RF is present, the red blood cells clump
together. This method is often used to confirm the presence of RF.
- Nephelometry test. This test mixes the blood being
tested with antibodies that cause the blood to clump if RF is present. A
light is shined on the tube containing the
mixture and the amount of light blocked by the blood sample is measured. As
levels of RF increase, more clumping occurs, causing a cloudier sample and less
light to pass through the tube.