Labs Labs are tools to help diagnose RA, distinguish it from other forms of arthritis, determine its severity and monitor key body functions for the liver and kidneys during treatment. Rheumatoid Factor (RF) Rheumatoid Factor is an autoantibody that is produced by the body’s immune system. Autoantibodies, made by the B cells, attack a person’s own antibodies. The presence of Rheumatoid Factor is an indicator of inflammatory and autoimmune activity. Elevated in about 80% of those diagnosed with RA. Some link the severity of RA with the degree of elevation. The RF may also be elevated in those with Lupus, endocarditis, cancer and a variety of other disorders. My RA is considered sero-negative as my RF factor was not elevated.