Antibody Tests Rheumatoid factor (RF)
One of the most common antibodies tested for. This is present in ~ 70-80% Rheumatoid arthritis (RA) but is also present in other diseases such as hepatitis, chronic liver disease, thyroid disease, certain infections, and other autoimmune diseases like lupus, Sjogren’s etc. Therefore the diagnosis of RA should not be based on a positive RF. Moreover RA can be ‘Sero-negative’ i.e. the patient can have RA but the RF test is negative. This is equally aggressive disease and can be confirmed using MSKUS (Musculoskeletal Ultrasound).
RF together with anti-CCP has a 95% sensitivity for RA. If RA is suspected both antibodies should be tested simultaneously (unless there are financial issues – then test RF first). If positive a Rheumatologist opinion must be sought.
Antibodies can be present a decade (10-years) prior to the development of the disease. So treatment decisions are very much clinical and should remain within the domain of the Rheumatologist.
Antibodies circulating in the blood are markers of disease, i.e. they indicate that the person has or will develop in the future an autoimmune disease. This is not necessarily true. Some people have antibodies positive on a blood test simply because they are relatives of people with autoimmune disease. Antibodies also develop with aging. The immune system clearance mechanisms decrease in efficiency as we age and this allows antibodies to develop and circulate in the blood.
Antibody tests are generally done once in a lifetime (if positive). They do not usually vary with disease activity except for some tests.
Antibodies can be present a decade (10-years) prior to the development of the disease. So treatment decisions are very much clinical and should remain within the domain of the Rheumatologist.