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
Interpretation
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