Rheumatoid factor (RF) ia an autoantibody that binds to the Fc portion of IgG. This binding can result in false positive results in tests that employ IgG antibodies (ELISA, latex agglutination, etc).
Examples of tests affected:
(1) troponin
(2) RPR
(3) HIV
(4) HCG
(5) Lyme disease
(6) hepatitis C
(7) sex hormone binding globulin
Ways to avoid false positive reactions:
(1) removing rheumatoid factor by precipitation or absorption onto aggregated human IgG
(2) decomposition of IgM by combining heat and beta-mercaptoethanol or dithiothreitol
(3) using reagents composed of the F(ab)2 fragments after removal of Fc
(4) developing antibodies in species that are not targeted by RF (chicken, etc).
Differential diagnosis:
(1) antibodies to animal antigens targeting antibodies prepared in different species
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