Rheumatoid Factor (RF) is an abnormal antibody made by human immune system which can bind to other healthy antibodies and destroy the function of patients’ normal immune system. High levels of rheumatoid factor in the plasma are most often related to autoimmune diseases, such as rheumatoid arthritis and Sjogren's syndrome. Therefore, RF is a more accurate and sensitive biomarker for diagnosing autoimmune diseases. In clinical research, the increase in serum secretion of RF has not be only indicated rheumatoid arthritis and Sjogren's syndrome, but also associated with a number of other diseases, e.g. Cancer, Chronic infections, Inflammatory lung diseases, Mixed connective tissue disease, Systemic lupus erythematosus. Thus, monitoring RF levels has a great clinic significance for general health screening, especially in older age group. The reference value of the RF in plasma is < 20 IU/ml.

This assay is a turbidimetric immunoassay for the quantitative measurement of rheumatoid factor in human serum and plasma. A standard or sample is added into a cuvette and mixed with the reaction buffer R1. After a short incubation, the test reagent R2, which is a suspension of microparticles coated with normal human IgG antibodies, of which Fc portion can be highly specific recognized by rheumatoid factor, is added into the cuvette and mixed. The presence of rheumatoid factor in the standard or sample causes the immune-particles to aggregate. The extent to which the microparticles aggregate is quantified by the amount of light scattering measured as absorbance by a chemistry analyzer. The concentration of rheumatoid factor in unknown samples can be interpolated from a reference curve using the standards provided.

TYPICAL STANDARD KITS

Assay procedures may vary depending on the automated chemistry analyzer to be used. A general example of assay procedures is stated as follow:

1. Dispense 150µl of R1 into a clean cuvette

2. Add 3µl of serum or plasma sample or rheumatoid factor calibrator and incubate at 37˚C for 5 minutes

3. Further add 50µl of R2

4. Read change of absorbance at 570 nm for 8 minutes after the addition of R2

5. Calculate the concentration of Rheumatoid factor in unknown sample by interpolation from a reference curve using the standards provided

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