Rheumatoid Factor

What is rheumatoid factor?

Rheumatoid factor (RF) is a type of antibody.

Usually, your immune system makes and uses antibodies to protect you. They’re special proteins that act like an army of security robots that find and destroy germs, allergens or toxins in your blood. When your immune system detects a new, unwanted substance in your body, it makes antibodies customized to find and destroy that invader.

Your immune system makes rheumatoid factor by mistake or when it’s overactive. Because RF doesn’t have a specific target like other antibodies, it sometimes attacks and damages healthy tissue throughout your body. This can cause some autoimmune diseases.

What are symptoms of high rheumatoid factor?

Which symptoms you experience vary depending on what’s causing your high rheumatoid factor level. Some people have high RF levels and never experience any symptoms. It’s also possible to have a high rheumatoid factor for no apparent reason or without a specific cause.

Where you experience symptoms and their severity depends on where your immune system damages healthy tissue in your body. Some of the most common symptoms of high rheumatoid factor include:

• Pain, especially joint pain.
• Swelling (inflammation).
• Skin discoloration.
• A feeling of warmth or heat.
• Fatigue (feeling tired all the time).
• Frequent fevers.

What is a rheumatoid factor test?

A rheumatoid factor test is a blood test providers use to measure how much rheumatoid factor is in your blood. They’ll take a sample of blood and send it to a lab for analysis. An RF test on its own can’t diagnose or confirm any health conditions you may have. But it can help your provider rule certain issues out or help them narrow in on a diagnosis.

When is this test performed?

A rheumatoid factor test can help a provider diagnose autoimmune diseases, including:

• Rheumatoid arthritis.
• Sjögren’s syndrome.
• Juvenile idiopathic arthritis.
• Lupus.
• Scleroderma.
• Mixed connective tissue disease.

Providers sometimes use RF tests to diagnose chronic (long-term) infections, including:

• Hepatitis C.
• Tuberculosis (TB).
• Infective endocarditis.

How do I prepare for a rheumatoid factor blood test?

You don’t need to do anything special to get ready for a rheumatoid factor blood test. You can eat, drink and do all your usual activities.

Your provider may take a sample of your blood during a routine physical exam or if you visit them after noticing new symptoms. They might ask you to visit a phlebotomist (blood draw specialist) at a separate appointment.

What happens during the test?

The RF test is just like any other blood draw you may have had before. Your provider or a phlebotomist will take a sample of your blood from a vein on the inside of your elbow or the back of your hand. Tell your provider if you don’t like needles or feel stressed during blood draws. They’ll help you relax and feel comfortable before and during the test.

Your provider or phlebotomist will:

• Clean the area with an antiseptic wipe.
• Put an elastic band around your upper arm that puts light pressure on it. They may ask you to make a fist or squeeze your hand, too. (Both actions encourage blood to flow to your arm and hand to make it easier to get a sample.)
• Gently insert a needle into your arm or hand. You might feel a sharp pinch. Try to keep your arm relaxed and breathe normally.
• Collect a sample of your blood in a vial.
• Remove the needle and put a bandage over the spot where they inserted it.

It’s less common, but your provider might have you do a rheumatoid factor test at home with a finger prick kit. You’ll poke the tip of your finger yourself with the provided needle (lancing device) and collect the blood on a special strip of paper. Follow all the directions that come with the RF test kit, including how to safely package and ship the sample.

What happens after the test?

After your provider or phlebotomist collects a sample of your blood, that’s it. You don’t need to do anything else. They’ll send the sample to a lab for analysis.

What are the risks of this test? Are there side effects?

There are very few risks to having a rheumatoid factor test.

Some people feel dizzy or lightheaded after a blood draw. You may need to rest a few minutes before standing up or moving. Even if you experience these side effects, they usually only last a few minutes at most.

What is a normal rheumatoid factor level?

Providers usually measure rheumatoid factor as a number that says how many units of RF are in each milliliter of your blood (U/mL). A normal, healthy amount of rheumatoid factor is less than 20 units per milliliter (<20 U/mL).

Your provider might also refer to your test as being negative or positive. A negative result means you have a normal amount of RF in your blood. Positive means you have high levels of rheumatoid factor.

It might seem confusing for negative to be a “good” test result, but that means your blood doesn’t show unusual changes (it’s negative for anything out of the ordinary).

What does a high rheumatoid factor mean?

Having a high rheumatoid factor can mean you have an autoimmune disease or another health condition. However, a rheumatoid factor test doesn’t diagnose anything directly, and having elevated RF doesn’t automatically mean you have rheumatoid arthritis (or any other condition). It’s just a clue your provider will use to diagnose what’s causing your symptoms.

A note from Cleveland Clinic

Rheumatoid factor is an antibody your immune system makes by mistake. A rheumatoid factor test is a simple blood draw your healthcare provider may use to help diagnose autoimmune diseases like rheumatoid arthritis and Sjögren’s syndrome.

Your provider will help you understand your test results and any conditions you may have. They’ll help you find a combination of treatments to manage your symptoms and reduce how often they affect your daily routine.