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Rheumatoid Factor

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What is Rf? Rheumatoid factor (Rf) and the measurement of this can aid in the diagnosis of rheumatoid arthritis. Is this a qualitative or semi-quantitative test? Both. So, in this simulation you will perform a qualitative Rf test and if positive perform a two-fold serial dilution to semi-quantitate the amount of Rf present.

Planning and Carrying Out Investigations


Rheumatoid Factor Brochure

Rheumatoid Factor Brochure

What is rheumatoid arthritis?

Rheumatoid arthritis (RA), an inflammatory process that results in the destruction of bone and cartilage. It affects about 0.5-1.0% of the adult population. It typically affects the age group of 25-55 and women are three times as likely to be affected than men.

What is the rheumatoid factor?

The rheumatoid factor (Rf) is an autoantibody, usually of IgM class, that reacts with the Fc portion of IgG.

How many patients with RA actually test positive for the Rf?

Approximately 70–90% of patients test positive for RF, so a negative result does not rule out the presence of RA.

Is a positive test result specific for RA?

No, a positive test result is not specific for RA, because Rf is also present in about 5% of healthy people and in 10–25% of those people over the age of 65.

Can Rf be found in patients with other connective tissue diseases?

Yes, Rf can appear in patients with other connective tissue diseases, such as SLE, Sjogren’s syndrome, scleroderma, and mixed connective tissue diseases.

What are the clinical signs and symptoms of RA?

A patient with RA may experience nonspecific symptoms such as malaise, fatigue, fever, weight loss and transient join pain that begins in the small joints of the hands and feet. Patients may also experience joint stiffness and pain usually present in the morning. Often, these symptoms improve as the day continues.

What other antibody besides Rf is found in patients with RA?

One other antibody, Anti-CCP (anticyclic citrullinated peptide antibody), is found in patients with RA. Both Rf and Anti-CCP are thought to combine with their specified antigen, forming immune complexes that are then deposited in the joints.

Does testing for both Rf and Anti-CCP provide a more accurate diagnosis of RA?

Yes, testing for both Rf and Anti-CCP provides a more accurate diagnosis of RA, giving a specificity of 98–100%.

What is the principle behind the Rf rapid test?

The Rf reagent is a suspension of polystyrene latex particles uniform in size and coated with human gammaglobulin or IgG. If Rf is present in the serum, the Rf will react with the IgG coated latex particles starting the process of agglutination. This reaction presents itself as clumping, which is then seen on the slide.

How is the titer determined in the Rf semi-quantitative procedure?

The titer in the Rf semi-quantitative procedure will correspond to the highest serum dilution showing agglutination or clumping and will be reported in IU/mL.

How much Rf is present if the initial qualitative test is positive?

If the initial qualitative Rf test is positive, then the titer is ≥10 IU/mL.

Tier 2 Lessons: Grades 7 - 12+

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Tier 2 Lessons: Grades 7 - 12+