Rheumatoid factor (RF) is an antibody, the presence of which can be observed not only in the body fluids of sick people, but also in he althy people. It is not an independent disease entity, but its presence or increased value exacerbates the course of many pathologies common in society.

What is rheumatoid factor?

Rheumatoid factor(Eng.rheumatoid factor-RF ) is an antibody that binds with the body's physiological IgG antibodies. About 85 percent of the cases are IgM-class, but there are also forms of IgA, IgG and IgE that are of little clinical significance.

By attaching to the FC fragment, more specifically the CH2 and CH3 domains, IgG antibodies lead to the activation of the complement system and the formation of immune complexes. These processes then lead to degenerative changes as a result of an active inflammatory process.

Its presence and increased levels in the body are correlated with the exacerbation of some rheumatic diseases, but it is not a specific indicator of any pathology. Its presence in the he althy population is 1-2 percent.

It grows with age and after 70 years of age, a significantly elevated titer in diagnostic tests is observed in 10-25 percent of the population of he althy people who do not experience any clinical symptoms associated with its presence.

It is possible to detect rheumatoid factor in synovial fluid, blood serum, and also in pleural or pericardial fluid.

RF - rheumatoid factor and rheumatoid arthritis

Rheumatoid factor influences the form of rheumatoid arthritis. It is found in synovial fluid in about 80 percent of patients with this chronic disease. The detection of this autoantibody in the blood serum is the basis for determining the seropositive form of the disease, which is the more severe form.

Its presence in people with RA leads to an erosive course of the disease, manifested within two years by degeneration of the joints, and its significantly increased level is associated with the occurrence of extra-articular symptoms.

The specificity of the rheumatoid factor for rheumatoid arthritis is50-90 percent, and the sensitivity is set at 60-70 percent. For this reason, its presence is not treated as an unambiguous criterion in diagnosing rheumatoid arthritis in a patient, but only as a factor that may influence the course of the disease and the treatment model.

RF - rheumatoid factor in non-rheumatic diseases

Rheumatoid factor can be detected in body fluids of people suffering from non-rheumatoid diseases, i.e .:

  • acute allergic alveolitis
  • autoimmune pancreatitis
  • large granular lymphocyte leukemia
  • autoimmune T-cell lymphoma
  • chronic inflammatory liver diseases
  • bacterial and viral infections

Its presence is sometimes false-positive in laboratory tests, the purpose of which is to detect and measure the levels of other proteins in the body. This situation can be observed when testing the level of cardiac troponins, which mistakenly suggests the destruction of the heart muscle cells.

RF - study

The rheumatoid factor in body fluids is detected by methods that depend on its class. We detect IgM class using:

  • Waaler-Rose reaction,
  • latex reaction,
  • laser nephelometry,
  • enzyme immunoassays.

RF Results

The Waaler-Rose testconsists in the incubation of the body fluid with the addition of sheep erythrocytes at a temperature of 37 degrees Celsius. The test is positive if there is agglutination in the titer<1:80.

Another test, calledlatex test , involves agglutination of rheumatoid factor coated on a latex molecule acting as a carrier with human gamma globulin. If agglutination occurs in the name<1:40 to próba uznana jest za dodatnią.

Resultlaser nephelometry- a method that uses the effect of light scattering by a colloidal solution - is positive for rheumatoid factor when it reaches the value of<40 j./ml.

Immunoenzymatic methods , such as ELISA, are used to detect rheumatoid factor not only in the IgM class, but also in the IgG, IgE, and IgA classes. The manufacturer of the test provides correct values ​​for a given test.

Rheumatoid factor and other rheumatic diseases

Rheumatoid factor is also detected in other diseases of connective tissue. In 60 percent of patients with Sjorgen's syndrome, its value exceeds physiological norms. Elevated titer of this autoantibody also occurs in 50 percent of patients with mixed connective tissue disease and is associated with severe inflammation.joints.

In some patients with ankylosing spondylitis, rheumatoid factor IgA is present, but it is not observed in IgM class. To a lesser extent, it is found in systemic lupus erythematosus and systemic scleroderma.

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