What is Rheumatoid Factor?

What is Rheumatoid Factor (RF)?

This is a great question as it is a very common test that we do in Rheumatology. Rheumatoid factor is a blood test that is done when we are trying to confirm whether a person has Rheumatoid Arthritis.

Rheumatoid Factor is an antibody in the blood that can be present in low levels in some people but is  elevated in most people with Rheumatoid Arthritis. However, it also occurs in other conditions such as Lupus and people without joint disease, so its presence doesn’t automatically mean that you have Rheumatoid Arthritis!

RF is an antibody targeting the body’s own immune system. Specifically, its an antibody to an antibody… it is an IgM antibody directed against an IgG antibody.

If I have Rheumatoid Factor, does that mean that I have Rheumatoid Arthritis?

Rheumatoid Factor is an antibody directed against the body’s own immune system. It is very strongly associated with Rheumatoid Arthritis, but just because the antibody is present, doesn’t mean that you will get or that you have Rheumatoid Arthritis.

RF is present in 1-2% of healthy people. In a country of 20 million people that would mean that approximately 40,000 people have it, and they don’t have any disease!

RF is also associated with other conditions, not just Rheumatoid Arthritis, so it is not a reliable screening test for Rheumatoid Arthritis. If it is present it can help to confirm the clinical diagnosis of Rheumatoid Arthritis, as Rheumatoid Arthritis is a clinical diagnosis, and not one that depends on laboratory testing.

Is the Rheumatoid Factor only associated with Rheumatoid Arthritis?

The Rheumatoid Factor is most strongly associated with Rheumatoid Arthritis with 80% of people with Rheumatoid Arthritis having the RF positive in the blood.

However, it is also associated with a number of other conditions such as:

  • Sjogrens disease
  • Chronic infections, such as Hepatitis B,
  • SLE (Lupus)
  • Scleroderma
  • Mixed Connective Tissue disease
  • Sarcoidosis
  • Cirrhosis
  • and sometimes cancer
If I have a high level of Rheumatoid Factor, does that mean something?

Rheumatoid Arthritis is a clinical diagnosis. The antibody for RF is only a confirmation of the diagnosis. Levels of antibodies in the blood in the absence of any disease have not been shown to be predictive of any disease.

However, if a diagnosis of Rheumatoid Arthritis has been made clinically and been confirmed by the presence of Rheumatoid Factor then very high levels of the Rheumatoid Factor at the time of diagnosis have been shown to be associated with having more serious disease.