Rheumatoid Factor

RF is one of several indicators of autoimmunity.

IgM autoantibodies; against Fc portion of IgG


Measured by latex fixation: reported by dilution with >1:40 being abnormal


An immunoglobulin directed against the Fc portion of IgG. It can be isotype IgG, IgA or IgM. Usually it is only IgM.


 new test - anti-cyclic citrullinated peptide

90-96% specificity

47-76% sensitivity

A positive result is > 20 i.u. 4-20% of healthy people have a detectable R.F, with increases seen in age. 75% of patients with established Rheumatoid Arthritis have a positive R.F, but only 30% in first three months. High levels correlate with disease severity. R.F. is also seen in other chronic immune diseases such as Sjogren’s Syndrome and hepatitis C.


can be type II (monoclonal IgM to polyclonal IgG) or type III (polyclonal IgM to polyclonal IgG)


make a table; rheumatic vs non-rheumatic