A rheumatoid factor (RF) blood test is done to measure the amount of the RF antibody present in the blood. In normal cases, antibodies are produced by the immune system to fight and destroy the bacteria and viruses which are capable of causing disease. But the RF antibody can attach to normal body tissue, resulting in damage. Several autoimmune diseases can become a reason for a high level of rheumatoid factor. Occasionally an elevated level of RF is found in healthy people. The method used to measure the RF is called the Nephelometry test.