Rheumatoid factor (RF)

Definition

Rheumatoid Factor (RF) is an autoantibody found in the blood that targets the Fc region of IgG antibodies. It is commonly used as a marker in the diagnosis of rheumatoid arthritis and other autoimmune diseases.

5 Must Know Facts For Your Next Test

1. RF is detected using agglutination assays, which cause visible clumping when RF binds to IgG-coated particles.
2. Elevated levels of RF are often associated with rheumatoid arthritis but can also be seen in other conditions like Sjögren's syndrome and chronic infections.
3. RF can be of different immunoglobulin classes, including IgM, IgA, and IgG, with IgM-RF being the most commonly tested type.
4. Not all patients with rheumatoid arthritis have a positive RF test; around 20-30% may test negative.
5. The presence of RF alone is not diagnostic; it must be interpreted alongside clinical symptoms and other laboratory findings.

Review Questions

Related terms

Agglutination Assay: A laboratory method used to detect antibodies or antigens by their ability to cause visible clumping of particles.

Autoantibody: An antibody produced by the immune system that mistakenly targets and reacts with a person's own tissues.

IgM:

A class of immunoglobulin that is often the first antibody to respond during an immune response and can form complexes leading to agglutination.