RHEUMATOID FACTOR

(RF)

• Rheumatoid arthritis is a chronic inflammatory disorder that affects all joints either in hands or feet and other areas of the body as the disease progresses.

• The disease affects the lining of joints, causing a painful swelling that can eventually result in bone erosion and joint deformity.

• The most common areas affected are :1.Tendons 3. Heart blood vessels2.Subcutaneous tissues 4. lungs

• RA is an autoimmune disorder, occurs when your immune system mistakenly attacks your own body's tissues. Characterized by inflammation of the synovial membranes and accumultion of synovial fluid in these membranes.

• Rheumatoid arthritis is a systemic disease, meaning it can affect the entire body.

Pathological changes during RA :• Formation of granulated tissue that

extends as vascular layer from the margin toward the center of effected joints.

• Generalized lymphadenopathy.• Toxemia.

Laboratory Finding during the disease :

• Elevated ESR , CRP• Changes in the serum protein• Hypochromic anemia• RF test is positive ( more than 1:8 titer).

• Rheumatoid factor is a typical serological findings in RA.

• RA and related diseases causes the production of globulin known as RF which is :

an autoantibody directed against the Fc portion of IgG and they can belong to IgM, IgG and any of these can be detected in the blood.

Clinical conditions also give Positive RF :• SLE ( Systemic Lupus

Erythematosus)• Systemic sclerosis• Mixed connective tissue disease• Multiple myeloma• Infectious mononucleosis.

That antibody binds to normal circulating IgG, forming immune complexes that are deposited in the joints. These immune complexes can activate the complement cascade, resulting in a type III hypersensitive reaction, which leads to inflammation of the joints.

• Direct agglutination testRF is detected in serum by their ability

to agglutinate with latex particles which is a qualitative method.

If the result is positive, then do serial dillution to determine the accurate titer of RF in the serum

( semi-quantitative method ).

Titer = 1:8 or more means Rheumatoid Arthritis.

Note that :-• The negative result from the direct

agglutination doesn’t rule out RA, and positive result is not specific for RA.

• An example for false negative result is a Prozone Phenomena which resulted from high antibody titer ,when the number of antibody binding sites is greatly exceeded the number of epitopes.

In this case ; It is advisable to dilute the serm for use, As the antibody concentration is lowered below the prozone, the reaction occurs.• Interfering Factors in the test :

1. High lipid or cryoglobulin give false +ve result.

2. High IgG level in patient serum also give false +ve result.

3. Activated complement.