Biomarker Menu


Download this assay page in pdf format.


Rheumatoid Factor Isotypes (IgA, IgG & IgM)

Analyte: Rheumatoid Factor Isotypes (IgA, IgG & IgM)

Specimen Type: Serum

Optimum Volume: 0.5 mL


2-8°C -20°C -70°C
2 weeks 2 months 6.5 years

Reporting units: RF-IgM - IU/mL, RF-IgG - U/mL, RF-IgA - U/mL

Method: ELISA

Biological or Clinical Significance:

RF describes an antibody (IgM, IgG and IgA) that is directed toward antigenic determinants present on human and animal IgG. RF-IgM activity is detected by latex agglutination, nephelometry, radioimmunoassay (RIA) or enzyme linked immunosorbent assay (ELISA), of which ELISA and RIA have been proposed as the best techniques to measure RF-IgM activity.

The diagnostic specificity (20%) and predictive value (10%) of an RF-IgM test for RA is low. The specificity and predictive value of the RF test may be increased, however, by simultaneously measuring the three RF isotypes: RF-IgM, RF-IgA and RF-IgG. When all three RF isotypes are elevated, the specificity and predictive value of RF testing improves substantially.

Principle of Test Method:

The RF3 assay is a solid-phase ELISA that employs the quantitative sandwich enzyme immunoassay principle. It is a test to aid the diagnosis of rheumatoid arthritis.


1.. Swedler W, Wallman J, Froelich CJ and Teodorescu M. Routine measurement of IgM, IgG, and IgA rheumatoid factors: High sensitivity, specificity, and predictive values for rheumatoid arthritis. J. Rheumatol 1997; 24:1037-1044.
2. Tencer J, Thysell H, Andersson K and Grubb A. Long-term stability of albumin, protein HC, immunoglobulin G, kappa- and lambda-chain-immunoreactivity, orosomucoid and alpha 1-antitrypsin urine stored at -20 degree C. Scand J Urol Nephrol 1997; 31:67-71.

Related Assays

Downloadable, Printable Biomarker Menus

Alphabetical Listing

Download PDF

Biomarker Category

Download PDF