Rheumatoid factor concentration

Method

Serum rheumatoid factor concentration by clinical immunoassay - nephelometry, turbidimetry or ELISA - reported as a titre in international units per millilitre. The isotype measured, IgM or total, is recorded on the edge.

The method is part of the endpoint identity. Studies measuring the same quantity by a different method are held as separate endpoints.

Notes

Its near-misses are CAT:outcome/c-reactive-protein and erythrocyte sedimentation rate: all three appear in the same rheumatoid arthritis meta-analyses, all three fall with benefit, and all three get called disease activity markers. The distinction changes interpretation - this is an AUTOANTIBODY TITRE reflecting serological phenotype and it moves slowly or not at all over a short trial, while the acute-phase reactants move within weeks, so a null here at 12 weeks is expected and is not evidence against an anti-inflammatory effect. Distinct also from anti-CCP antibody, a different autoantibody with different specificity, and from the DAS-28 composite clinical index.