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What is the rheumatoid factor test?

The rheumatoid factor test is used in the diagnosis of illnesses like rheumatoid arthritis and Sjögren’s syndrome.

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 diseases, 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 antibodies.

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):

  • Less than 60 u/ml (when using nephelometry)
  • Less 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 disease.

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.

Arthritis, Diagnosis, Diagnosis, Scientific research, Health professionals, Public Healthcare, Private Healthcare

Author: Purificación Salgado, Journalist

Last Modification: November 7, 2016

© People Who Global, iStock.com, Monthian

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