Rheumatoid Factor Blood Test (RF)

Rheumatoid factor (RF) is an autoantibody that can be present in the blood of people with rheumatoid arthritis and several other inflammatory or autoimmune conditions. This test measures the level of RF in a simple blood sample and is most often requested when someone has ongoing joint pain, swelling, or stiffness, particularly in the hands and feet, or when a clinician is investigating a suspected autoimmune or inflammatory disorder.

It is important to understand that a positive RF result does not confirm rheumatoid arthritis on its own, and a negative result does not exclude it. RF can also be found in other conditions such as Sjögren's syndrome, systemic lupus erythematosus, chronic infections, and some liver diseases, and it may be present at low levels in a small proportion of healthy people, especially older adults. For this reason, RF is interpreted alongside your symptoms, a physical examination, and other tests such as inflammatory markers and anti-CCP antibodies.

Autoantibodies
- Rheumatoid factor (RF): an antibody directed against the body's own immunoglobulins, commonly measured to support the assessment of rheumatoid arthritis and related autoimmune conditions.

Why it matters
Measuring RF gives your clinician an important piece of the diagnostic picture when joint inflammation or an autoimmune condition is suspected. It can help guide further investigation, support a diagnosis when combined with clinical findings, and inform decisions about monitoring and treatment. Because RF results must always be considered in context, your doctor will discuss what your result means for you and whether any additional testing is appropriate.