Rheumatoid factor, what role does it play in arthritis?
Rheumatoid factor can play a key role in diagnosing illnesses such as arthritis or Sjögren syndrome. Discover why.
A rheumatoid factor test is a blood
test used to measure the amount of rheumatoid factor (RF) antibodies in your
blood. As RF antibody levels tend to be elevated in people with certain types
of rheumatic illnesses like arthritis or Sjögren’s syndrome, the RF test can be
extremely useful in helping the doctor to arrive at a diagnosis.
However, seeing as the results often
come back negative during the first few months, the test isn’t considered to be
effective if you’re looking for an early diagnosis. It’s also interesting to
note that even healthy people can, on occasion, test positive for RF
Why is the test used?
The rheumatoid factor test is an
immunological and serological test. It measures the presence and concentration
of immunoglobulin M and immunoglobulin G. Up to 70% of people with rheumatoid
arthritis will test positive during a RF test.
The presence of immunoglobulin G and
elevated levels of immunoglobulin M results in the formation of IgG-IgM immune
complexes. These, in turn, activate inflammatory factors which gradually
destroy the affected joints. This process is the reason why arthritis is
considered to be an autoimmune disease.
What does the test involve?
The RF test is a straight-forward
blood test that doesn’t require any kind of special preparations. You don’t
even have to fast before the test. It’s simply a matter of taking a blood
sample from a vein in the crook of your elbow or the back of your hand and
sending it to be tested for antibodies.
What do the results mean?
Normal levels (or a negative test result):
than 60 u/ml (when using nephelometry)
than 1:80 titer (when using agglutination)
Generally speaking, if your results
fall into either of the above two categories, it means you do not have
rheumatoid arthritis, although some people with the illness are known to have a
normal reading (known as a ‘false negative’).
An abnormal reading means the test is positive. In other words, the test has revealed high levels of the rheumatoid
factor in your blood – making it highly likely you have either rheumatoid
arthritis or Sjögren’s syndrome. The higher the reading, the more likely you
are to have one of the conditions. However, in the same way some people
register a false negative, others register a false positive – so the fact that
your results have come back positive is not, in itself, conclusive proof that
you have either of the illnesses.
Abnormal RF readings have also been
associated with a variety of other illnesses, including systemic lupus
erythematosus, dermatomyositis (DM), sarcoidosis and mixed cognitive tissue
Whatever the case, as useful as this
particular test is, it does not provide definitive proof of a diagnosis of
arthritis. A positive result is only considered to be conclusive when it is
backed up by the results of a physical exam and additional biomarker testing.
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