Rheumatoid factor

🏾 Rheumatoid factor normal range

The laboratory must report quantitative values expressed in IU/ml. A positive/negative result is of little importance.

Although "normal" rheumatoid factor values may vary from one technique to another, it is generally accepted that values >20 IU/ml are considered high.

🏾 Rheumatoid factor blood test

In general, there are no special preparations to make before the test, it is a routine blood test that can be done at any time and does not require fasting, unless your blood sample will be used for additional tests (e.g. blood sugar).

A healthcare professional will take a sample of blood from a vein in your arm, using a small needle.

🏾 Interpretation

High rheumatoid factor

High levels of rheumatoid factor in the blood are most commonly associated with autoimmune diseases, such as rheumatoid arthritis and Sjogren's syndrome. But :

There are several causes of high rheumatoid factor levels: Certain types of cancer, including leukemia, mononucleosis, tuberculosis, inflammatory lung diseases, such as sarcoidosis, mixed connective tissue disease, Sjogren's syndrome, lupus, juvenile arthritis , scleroderma, hepatitis C, etc.

Note: Rheumatoid factor assay also has a prognostic value. A high level of rheumatoid factor greater than three times the laboratory positive threshold is a sign of a poor prognosis.

Low rheumatoid factor

A negative result does not exclude the diagnosis of rheumatoid arthritis.

Rheumatoid factor may decrease or even become negative during the course of the disease after initiation of treatment

🏾 Assay techniques

Waaler-Rose reaction : agglutination of sheep red blood cells, or ORh– human red blood cells, sensitized with rabbit IgG.

Latex reaction : agglutination of latex particles coated with human IgG.

Immunoenzymatic methods : They are based on the principle of ELISA or dot, depending on whether the human and/or animal IgGs have been fixed to the bottom of the microtiter plate well or to a membrane. The revelation is done with an anti-IgM antiglobulin marked by an enzyme.

Nephelometric method : binding of RF to polystyrene particles sensitized by human or human and animal ã-globulins, or to aggregated ã-globulins: the intensity of the scattered light is measured by nephelemetry, it is proportional to the concentration of EN in serum

🏾 What other tests could I have with this test ?