If you’ve recently had a rheumatoid factor (RF) test, you might be wondering: What do these numbers mean? Is my Rheumatoid Arthritis (RA) better or worse?

RF is an autoantibody that can play a role in diagnosing RA, but it’s only part of the bigger picture. What is an antibody, you might ask. Antibodies are proteins in your body that help protect you by fighting off germs and keeping you from getting sick. An RF antibody is like a tiny soldier in your body that sometimes gets confused and starts attacking your own joints instead of germs, which can make them hurt and swell.

Understanding your RF test can help you have better conversations with your clinician and play an active role in your care. Understanding your RF levels — whether positive or negative — can help you and your clinician make informed decisions about your diagnosis, treatment, and long-term RA management.

In this article, we’ll break down what your RF test results mean, how they fit into your overall RA diagnosis and treatment plan, and what questions to ask your clinician to make the most of your care. It is important to remember that RF is only one of several biomarkers used. 

Understanding Rheumatoid Factor and its Role in RA 

How is the RF Test Performed?

A rheumatoid factor test is a simple blood test that requires no special preparation. During the test, a healthcare provider draws a small sample of blood. The sample is then sent to a lab; results are typically available within a few days. RF levels are reported as a number, but since values can vary between specific laboratories, your clinician can help interpret the results for your health.

Why is RF Measured?

Positive RF levels alone are not enough for a definitive diagnosis of RF since false positive results can occur. High RF levels may provide useful insights to your clinician, especially when combined with symptoms and other lab findings. 

RF Testing in Combination with Other Tests Can:

• Help support an RA diagnosis
• Differentiate between seropositive and seronegative RA
• Guide treatment decisions

Interpreting Your Rheumatoid Factor Test Results 

How RF Levels are Measured 

Jeffrey Curtis, MD, MS, MPH, a rheumatologist and Professor of Medicine in the Division of Clinical Immunology and Rheumatology at the University of Alabama at Birmingham, explains how to interpret RF levels.

“Rheumatoid factors are usually measured in units per milliliter, and different laboratories may have somewhat different reference ranges. Many laboratories consider RF positive if it’s above 14 to 20 units per milliliter, and higher numbers may indicate worse disease or worse outcomes. Some people have a mildly elevated RF without having rheumatoid arthritis.”

Does my RF Level Confirm RA, or do I Need Additional Tests?

“A positive RF lab test supports an RA diagnosis,” explains Dr. Curtis. “When combined with other clinical signs and symptoms, between 60 and 80 percent of RA patients will have a positive rheumatoid factor test and be so-called seropositive. That said, a patient can have a positive RF test and not have any kind of arthritis.”

A positive RF test alone isn’t enough to diagnose RA. Your clinician will consider other factors, including your symptoms and additional tests, to get a complete picture of your health. Some of the tests your clinician may order include:

• Anti-Cyclic Citrullinated Peptide Antibodies (Anti-CCP): More specific for RA than RF.

• C-Reactive Protein (CRP) & Erythrocyte Sedimentation Rate (ESR): Measures inflammation.

• Imaging (X-ray, Ultrasound, MRI): Helps assess joint damage. 

“Part of the role of the rheumatology provider is to integrate results from this and other blood tests with your symptoms, physical exam findings, and imaging results,” according to Dr. Curtis.

What’s the Difference Between Seropositive and Seronegative RA?

Seropositive RA (RF Positive): Seropositive RA means that a person’s blood has certain markers that show their immune system is attacking their own body, especially the joints. These markers are found through a blood test. If you are seropositive, then you have RF and/or anti-CCP antibodies in your blood. This form of RA is more common and may be more aggressive.

Seronegative RA (RF Negative): Seronegative RA means that a person has arthritis where their immune system is still attacking their joints, but their blood doesn’t have the usual markers found in seropositive RA. However, even without those markers, clinicians can still see signs of joint damage in imaging tests, swelling and pain, and use other tests to confirm your diagnosis and help you manage the symptoms. If you are seronegative, you do not have detectable RF in your blood, but you still have symptoms of RA. Diagnosis may rely more on symptoms and imaging. 

Seronegative patients are more likely to be diagnosed based on symptoms, imaging, and inflammatory markers rather than antibody tests. 

Should I Be Retested for RF in the Future?

If someone is RF negative at the time of initial diagnosis, they usually will stay negative, but a small fraction of people may turn positive.  

Your clinician may check your RF level again if you were initially negative, but ongoing RA monitoring is based on symptoms, inflammation markers, and imaging. 

How RF Affects RA Treatment and Long-Term Management 

If my RF is High, Does it Mean my RA is Worse?

A high RF level may indicate more active disease, but it’s not the only factor. Your symptoms, inflammation markers, and imaging results give a more complete picture. Higher RF levels may be associated with more severe RA symptoms, including joint erosion and extra-articular complications. Extra-articular means that the problem isn’t just in the joints but also in other parts of the body (such as lung or cardiovascular involvement). However, effective treatments can help manage symptoms and prevent long-term damage. Regular follow-ups with your provider can ensure your treatment is working and adjusted as needed. 

Are There Treatment Options That are Better for me Based on my RF Level?

Certain medications, such as biologics, may work differently depending on whether a patient is RF-positive or RF-negative. Some research suggests that certain treatments may be more effective in RF-positive patients. However, Dr. Curtis emphasizes that “rheumatoid arthritis treatment overall is based on symptoms, levels of inflammation, and joint damage, not just the rheumatoid factor blood test result.”  

Blood tests are just one piece of the bigger picture when determining the best treatment approach. Your clinician will consider: 

• RF status
• Other lab results
• Genetics and lifestyle factors
• Comorbidities (other health conditions)
• RF and ongoing RA management 

Monitoring Your Symptoms

What Else Should I Track to Monitor my RA?

• Monitor your symptoms: Keep a note of your pain, stiffness, and swelling, including things like when these symptoms flare, how long they last, and when you feel better. 

• Track and know your inflammation markers— CRP and ESR; these can provide key information about swelling inside your body. 

• Track your joint health through imaging (ultrasounds, X-rays, and scans). 

How Can I Lower my Risk for RA Complications?

• Stay active: Gentle exercise may help maintain joint function even though movement for those with RA can be difficult and painful. 

• Follow your treatment plan: Sticking to prescribed medications may help prevent joint damage. 

• Manage comorbidities: Conditions like heart disease and osteoporosis can be linked to RA. Regular check-ups and working closely with your healthcare team are important to keep both your RA and any other health issues under control. 

What Should I do if my Symptoms Change?

• If you notice new or worsening symptoms, make sure to track them and share the details with your clinician. This will help them adjust your treatment plan and ensure you’re getting the best care for your RA. 
• Request follow-up tests if you notice significant pain, swelling, or mobility changes. 

What Are the Warning Signs That My RA Is Worsening?

• Increased joint pain and swelling. 

• New joint deformities or changes in the shape of your joints. 

• Feeling more tired and stiff for longer periods of time. 

Talking with Your Clinician: Using RF to Guide Your RA Care

You can use your rheumatoid factor results to kick-start a conversation with your clinician.  A few key questions to ask your clinician include: 

Understanding the Test Results 

• What does my RF level mean in the context of my symptoms? 
• Do I need additional tests to confirm my RA diagnosis? 

Impact on Treatment Options 

• Does my RF status (positive or negative) affect my treatment plan? 
• Are there certain medications that may work better for me based on my RF level? 

Monitoring Disease Progression 

• Besides RF, what other factors should we track to monitor my RA? 
• If I’m already on treatment, how do we assess whether it’s working? 

Overall Disease Management 

• What symptoms or changes should I watch for that might indicate my RA is worsening? 
• How does my RF level result fit into the bigger picture of managing my condition? 
• What lifestyle changes or self-care strategies can help manage my RA symptoms? 

Putting the Pieces Together to Better Manage Your RA

Your RF level is just one piece of the RA puzzle. While it provides useful insight, your overall health, symptoms, and other test results are just as important in shaping your treatment plan. By tracking your health data, asking informed questions, and working closely with your clinician, you can take an active role in managing your RA symptoms and making decisions that support your overall well-being. 

Content for this podcast/article was developed by the GHLF. Financial support was provided in part by UCB, Inc.