What Is the Rheumatoid Factor Test?
A rheumatoid factor test, or RF test, is a blood test to look for rheumatoid factors in your blood.
If you have symptoms of rheumatoid arthritis, such as pain, swelling, and stiff joints, your doctor may use the rheumatoid factor blood test to help diagnose it. When rheumatoid factor is in your bloodstream, it will help your doctor know if you have rheumatoid arthritis and how severe it is. The test also helps your doctor tell the difference between rheumatoid arthritis and other types of arthritis, as well as other conditions.
High levels of rheumatoid factor can show up in people with severe rheumatoid arthritis. But even if the test results show you have a high level of it, your doctor will want to do other tests before they make a diagnosis. They will examine you and may order other types of lab tests, such as X-rays, a magnetic resonance imaging (MRI) scan, an ultrasound, or other scans.
What Is Rheumatoid Factor (RF)?
Rheumatoid factors are antibody proteins your immune system makes. Normally, your immune system makes antibodies to attack infectious invaders to keep you well. But rheumatoid factor antibodies are made by mistake and don’t have a specific or known target. As a result, they may attack your own cells or tissues to cause rheumatoid arthritis, an autoimmune condition that causes joint damage and pain, or another autoimmune condition.
What Is the Rheumatoid Factor Test Used For?
Your doctor may order a rheumatoid factor test if you have signs or symptoms that may be related to high levels of rheumatoid factor. But you could have high RF levels without any symptoms you notice. You could have high RF levels with no clear reason or cause. Some symptoms that might make your doctor wonder about your RF levels include:
- Joint pain
- Other pain
- Swelling
- Changes in your skin color
- Warmth or heat in your joints
- Fatigue
- Fevers
Rheumatoid factor tests may be used to test for rheumatoid arthritis. But an RF test also can help to diagnose other autoimmune conditions such as:
- Sjogren’s syndrome
- Juvenile idiopathic arthritis
- Lupus scleroderma
- Mixed connective tissue disease
RF tests may also be used to diagnose a chronic infection such as hepatitis C, tuberculosis (TB), or endocarditis.
- Related:Video: See How to Ease Hand Pain With RA
RF Test and Rheumatoid Arthritis Diagnosis
Nobody knows what the antibodies known as rheumatoid factor do when they’re in the blood of healthy people. It’s not clear exactly what they do when you have rheumatoid arthritis either. Most people with this form of arthritis will have RF in their blood. But you may not have a positive RF test if your rheumatoid arthritis is in an early stage. RF levels might change over time along with your disease activity. But even people who are in remission after treatment for their arthritis can still have high RF levels.
Rheumatoid factor also may be present in many or most people with other autoimmune conditions. So the presence of RF alone doesn’t mean that you have rheumatoid arthritis. You may not have signs of any autoimmune condition. Or you could have another condition that’s affecting your immune system.