Rheumatoid factor (RF) levels above a normal range can indicate autoimmune conditions, such as rheumatoid arthritis (RA).
Rheumatoid factor (RF) is an immune system protein that attacks healthy cells. An RF test is a blood test that can help diagnose rheumatoid arthritis.
While high RF levels can indicate rheumatoid arthritis, this is only one aspect of a complete diagnosis. High RF levels can also occur in people with other conditions and those without diagnosable health issues.
This article discusses RF testing, normal RF ranges, and what abnormal levels mean.
RF is an autoantibody, which is a type of self-reactive protein that the immune system produces.
In people with autoimmune conditions, the immune system mistakes healthy cells for foreign bodies and typically creates higher levels of antibodies, such as RF, to attack these cells.
Higher levels of RF in the body can indicate that some level of autoimmune activity is occurring, which can indicate an underlying condition.
As a result, an RF test is one test that doctors use to help diagnose autoimmune conditions.
The onset of rheumatoid arthritis and other autoimmune conditions, cancers, and bacterial infections can all affect RF levels, which may be difficult to assess in isolation.
The typical range for RF is usually 0–20 units per milliliter (U/ml) of blood. A person’s risk of developing rheumatoid arthritis typically increases with their RF level and the presence of another autoantibody CCP.
Many people with RA have significant concentrations of RF in their blood. Higher levels of RF can also occur in other conditions. For instance, autoantibodies can occur as part of natural aging or following some infections.
How high a person’s RF levels are will factor into a doctor’s diagnosis. Very high levels indicate more rheumatoid arthritis than lower levels, which means more immune system activity.
A high concentration of RF can be a sign of inflammation and autoimmune disruption. A person’s symptoms will depend on what condition accompanies the high RF levels.
For example, a person with high RF levels accompanying rheumatoid arthritis may experience:
- pain and stiffness in the joints
- swelling and inflammation in the joints
- a loss of range of motion
- nodules under the skin
- general fatigue
The RF test is a simple blood test.
A doctor takes a small sample of blood from a vein in a person’s arm and sends it to a laboratory, where a technician measures the levels of RF.
The results may not come back for several days. When they do, the doctor discusses them and the next steps with the person.
If a doctor suspects rheumatoid arthritis, they often order other blood tests alongside or after an RF test. These may include:
Learn more about blood tests for rheumatoid arthritis here.
While high RF levels may indicate rheumatoid arthritis, in many instances, this condition is not the only reason a person might have high RF levels.
Many other conditions can cause higher RF levels, including:
- Sjögren’s disease
- lupus
- chronic bacterial infections, such as syphilis or tuberculosis
- viral infections, including hepatitis C, HIV, and herpes
- parasitic infections, such as malaria
- cancer
- sarcoidosis
- cirrhosis
When a doctor tests for RF levels, they may also perform an anti-CCP test. Anti-CCPs are antibodies the immune system also produces.
If the results of both tests are negative, but a person is still showing other arthritis symptoms, they may have seronegative arthritis.
People with seronegative arthritis are typically at lower risk of severe disease progression and developing other complications. However, seronegative arthritis is still a serious condition that can require medical management and treatment.
People with seronegative arthritis may also develop other serious forms of arthritis, such as gout.
Learn more about seronegative rheumatoid arthritis here.
Treatment for high RF levels depends on the underlying cause.
For example, in people with rheumatoid arthritis, Sjögren’s disease, and other chronic conditions, treatment aims to slow the condition’s progression and help prevent or reduce symptoms such as inflammation.
On the other hand, if a bacterial infection is causing an increase in RF levels, a doctor may prescribe medication to treat the infection, which may result in decreased RF levels.
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Rheumatoid factor is a protein that the immune system produces. Some autoimmune conditions, notably rheumatoid arthritis, cause high levels of RF in the blood. Doctors measure a person’s RF levels to help them diagnose rheumatoid arthritis or another condition.
A high RF test result can indicate the presence of rheumatoid arthritis. However, this is not the only cause, and some people without an autoimmune condition can also have high RF levels. Doctors need to see various test results, consider a person’s clinical history, and perform a physical examination to diagnose rheumatoid arthritis.
Anyone who suspects they have rheumatoid arthritis or another autoimmune condition should contact a doctor.