Rheumatoid factor

Martina Feichter studied biology with an elective subject pharmacy in Innsbruck and also immersed herself in the world of medicinal plants. From there it was not far to other medical topics that still captivate her to this day. She trained as a journalist at the Axel Springer Academy in Hamburg and has been working for since 2007 - first as an editor and since 2012 as a freelance writer.

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Doctors refer to special antibodies as rheumatoid factor (RF).If it is found in the blood, it suggests an autoimmune disease such as rheumatoid arthritis. However, there are also other diseases and healthy people in which the rheumatoid factor can be increased. Read more about this blood value, when it is determined and what informative value the rheumatoid factor has!

What is the rheumatoid factor?

The rheumatoid factor is a so-called autoantibody. These are antibodies of the immune system that attack the body's own tissue and can thus trigger a disease (autoimmune disease). As the name suggests, rheumatoid factors play a role especially in autoimmune rheumatism.

Rheumatoid factors attack certain parts (Fc section) of other antibodies - namely the immunoglobulin G. They are practically antibodies against antibodies.

Depending on their structure, rheumatoid factors - like all antibodies (immunoglobulins) - are divided into different classes. These include, for example, immunoglobulin M (IgM), immunoglobulin A (IgA) and immunoglobulin G (IgG). As a rule, the detected rheumatoid factors belong to the IgM class (RF-IgM or RhF-IgM).

Studies indicate that above all high rheumatoid factor values ​​of the IgA class (RF-IgA) are related to more severe courses of rheumatoid arthritis (especially pronounced joint involvement and rapid joint destruction). The same is reported for IgG rheumatoid factors (RF-IgG). In addition, studies have shown that special drugs, so-called TNF-alpha blockers such as infliximab, are less effective in patients with high RF-IgA levels in the blood.

When is the rheumatoid factor determined?

The doctor determines rheumatoid factors if a rheumatic disease is suspected - especially rheumatoid arthritis. However, a positive test result alone is not sufficient for the diagnosis. The RF is not a very specific laboratory value - it can be increased in various rheumatic diseases, but also non-rheumatic diseases or in healthy people.

For the examination, the doctor takes a blood sample from the patient. The rheumatoid factor is usually measured in the blood serum. Laboratory physicians can use various techniques for detection (e.g. ELISA, radioimmunoassay). Depending on the measurement method, different limit values ​​apply, and if they are exceeded, one speaks of an increased rheumatoid factor.

When is the rheumatoid factor increased?

The rheumatoid factor is particularly high in rheumatoid arthritis. At the beginning of the disease, almost half of the patients are rheumatoid factor positive. In the further course of rheumatoid arthritis, around 70 to 80 percent of those affected have elevated levels of rheumatoid factor of the IgM type (RhF-IgM) in the blood (seropositive rheumatoid arthritis). Conversely, this means: One can have rheumatoid arthritis even without evidence of rheumatoid factors in the blood (seronegative rheumatoid arthritis).

The rheumatoid factor is just one of several parameters that are used to diagnose the disease.

Rheumatoid factor in rheumatism

In addition to rheumatoid arthritis, the test for rheumatoid factors can also be positive for other rheumatic diseases, i.e. it can provide increased measured values. These include, for example, the following diseases (in brackets the proportion of patients who are rheumatoid factor-positive):

• Cryoglobulinemia: a form of vascular inflammation (50 to 100 percent)
• Sjogren's syndrome (70 to 95 percent)
• Systemic lupus erythematosus (15 to 35 percent)
• Mixed collagenosis: disease with symptoms of various autoimmune-related connective tissue diseases such as systemic lupus erythematosus, scleroderma and polymyositis as well as Raynaud's syndrome (50 to 60 percent)
• Scleroderma (systemic sclerosis): collective term for autoimmune diseases that are associated with hardening of the connective tissue (20 to 30 percent)
• Juvenile chronic arthritis (10 to 15 percent)
• Polymyositis and dermatomyositis (5 to 10 percent)

Other causes

Elevated rheumatoid factor values ​​can also be found in people who do not have a rheumatic disease. This is possible, for example, in the following cases:

• Cirrhosis of the liver
• Chronic inflammation of the liver (chronic hepatitis)
• Chronic inflammatory lung diseases
• Inflammation of the lining of the heart (endocarditis)
• tuberculosis
• salmonellosis
• Sarcoid
• syphilis
• Acute infections with bacteria, viruses or parasites (e.g. glandular fever, malaria)
• Malignant tumors
• After blood transfusions
• After vaccinations
• After chemotherapy or radiation therapy

Last but not least, the rheumatoid factor can be detected in around five percent of healthy people - without any disease value. Above all in old age, many otherwise healthy people are RF-positive (around ten percent of those over 60).

An increased rheumatoid factor without any symptoms is of no importance.

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