Rheumatoid factor

Rheumatoid factor (RF):
Autoantibodies directed against the Fc fragment of IgG – positive in 75-90% of those with rheumatoid arthritis. Changes in RF do not reflect changes in activity of rheumatoid arthritis.
High frequency of false positive – present in 2-20% of normal population.
Most labs use agglutination of IgG coated particles as test.

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