Understanding Rheumatoid Arthritis Lab Tests and Results

Rheumatoid arthritis (RA) is a chronic autoimmune disease that primarily affects the joints, but can affect other parts of the body. Diagnosing and managing RA involves clinical evaluation by a rheumatologist, as well as several different laboratory tests that require blood work. The results of these tests may be used in two ways:

The doctor and healthcare team use the results of these tests to guide treatment options for each patient. In turn, understanding how the results of blood tests used to monitor RA and its treatment can help patients better able to manage their RA.

What is rheumatoid factor?

Rheumatoid factor (RF) was the first autoantibody to be discovered in people with RA. (Autoantibodies develop in response to the body’s own tissue, and are characteristic of autoimmune diseases, such as RA.) Despite the name, however, RF is not specific to RA, and there are many factors that can impact RF lab results. About 20% of those with confirmed RA will not have an abnormal RF test, while 5% of people who do not have RA will have an abnormal RF test. Negative levels do not exclude the disease, and positive levels do not guarantee the diagnosis.

The normal range of RF is from 0-20 IU/ml. RF above 20 IU/ml is not considered enough to diagnose RA, as there other reasons the RF level may be elevated. Some conditions and medical procedures that can raise RF levels include: other autoimmune diseases, certain chronic infections, diabetes, bacterial endocarditis, cancer, normal aging, vaccinations and transfusions. It’s important to note that once the RF level is elevated, it will often remain so even if the disease goes into remission.

What is anticyclic citrullinated peptide?

In addition to rheumatoid factor, another test which is ordered when rheumatoid arthritis is suspected is the anticyclic citrullinated peptide (anti-CCP). The normal level of anti-CCP is less than 20 Units. (At Hospital for Special Surgery, anti-CCP is reported in Units. Some labs report this same result using a different measurement notation, that is, as less than 20 EU/ml.) A level above 20 suggests the possibility of RA. As with rheumatoid factor, some people with positive anti-CCP antibody will not have RA, but this test is somewhat more specific for RA than the rheumatoid factor. The higher the levels of anti-CCP antibody, the more likely it is to suggest RA.

This test is 97% specific for RA if it is present. Once a patient develops a positive anti-CCP, it will usually remain positive, despite remission.

About 20% of RA patients are seronegative, meaning that their RF and anti-CCP lab results both continue to come back negative. In these cases, the physician makes the diagnosis based on physical examination and imaging.

RF and anti-CCP are not used to monitor disease activity, because they both tend to remain positive despite remission. Once the diagnosis of RA has been made and confirmed, these tests are not repeated.

What is sedimentation rate?

Sedimentation rate (also known as erythrocyte sedimentation rate or ESR), is a crude measure of inflammation. It is calculated by measuring the rate at which red blood cells sediment in a test tube in one hour. Normal levels for men range from 0-15 mm/hr to 0-20mm/hr and for women 0-20 mm/hr/ to 0-30mm/hr, depending on age – higher for people over the age of 50). The ESR rate is not specific for RA, and there are many factors that can interfere with the results, such as bad processing, an infection, and aging in patients over the age of 50.

What is C-reactive protein?

C-reactive protein is a measure of clinical inflammation often used in addition to an ESR. The normal measurement is less than 1.0 in many labs. This test, however, can be influenced by factors such as obesity and infection and is not specific to RA.

Both ESR and C-reactive protein are non-RA-specific measures of inflammation. Both tests are used to test disease activity; when they are high, this suggests that the disease is very active (assuming no other causes for high results, such as infection, are present). The healthcare team orders these labs regularly to monitor the patient’s disease and check how his or her medications are working.

What is complete blood count?

A complete blood count (CBC) test looks at red and white blood cell counts. Below are the normal measurements in our lab – other labs may well have their own set of normal values.

Test
White cell blood count (WBC)
Red cell blood count (RBC)
Hematocrit
Hemoglobin
Platelets

The CBC tests help to inform the healthcare team about side effects of treatment and any secondary consequences of RA, such as anemia. If the patient’s hemoglobin levels indicate anemia, this will be further investigated looking for its cause.

What is a complete metabolic panel?

A complete metabolic panel is used to monitor kidney and liver function, in order to assess whether changes to medication must be made or whether they are working well. A complete metabolic panel measures sodium (Na), potassium (K), chloride, glucose, creatinine (a measure of kidney function), and AST and ALT (markers of liver function).

Both the CBC and the complete metabolic panel are used to monitor disease activity as well as side effects and efficacy of medication.

With these laboratory tests as a guide, the healthcare provider may need to make adjustments to the patient’s medications and RA treatment. Laboratory tests provide important information in the diagnosis, management and treatment of rheumatoid arthritis. By becoming informed about the normal values for tests, as well as their own numbers, patients with RA can better communicate with the health care team and gain a better understanding about some of the information that is used in developing and monitoring their treatment plans.

Learn more about the HSS Early RA Support and Education Program, a free support and education group, developed specially for people recently diagnosed with RA and early RA.

Original summary written by Lysa Petrsoric, MPH, MSW, April 20, 2015, and edited by Nancy Novick.
September 2020 review by Theodore R. Fields, MD, FACP.

Authors

Monica Richey, MSN, ANP-BC/GNP
Mary Kirkland Center for Lupus Care, Hospital for Special Surgery

Related articles

RF Test: What is the Normal Range for a Rheumatoid Factor Test?

The rheumatoid factor is an antibody present in the blood of many patients with rheumatoid arthritis. Doctors measure the level of rheumatoid factor by performing a blood test. A positive rheumatoid factor test means that the level of rheumatoid factor in the patient’s blood is considered to be high.

Rheumatoid factor was first described in connection to rheumatoid arthritis in 1940. For decades, a positive rheumatoid arthritis test was used to diagnose those with symptoms of rheumatoid arthritis.

Today, a positive rheumatoid factor test is mostly used as a supportive tool to help doctors reach a diagnosis. Because rheumatoid factor may be present in other conditions, and in some healthy people, the test for it should be combined with other tools and criteria for it to be useful in diagnosis. A positive rheumatoid factor test is also used to determine a general prognosis for rheumatoid arthritis in adults and children.

What is Rheumatoid Factor?

The immune system is an organized method through which the body fights off infections caused by bacteria, viruses and other organisms. A normal immune response to infection often involves the production of proteins such as antibodies to kill these invading organisms.

Sometimes, however, certain antibodies produced by the immune system may attack healthy proteins. In other words, the antibodies turn against the person’s body damaging their health in the process.

When this occurs, the immune response that is triggered may result in what we now know as an autoimmune disorder. A variety of conditions have been shown to occur from these autoimmune responses.

Rheumatoid factor is one of many antibodies that are known to attack healthy tissue through an autoimmune process. When triggered, rheumatoid factor antibodies attack the healthy tissue resulting in a variety of symptoms.

Typically, these symptoms cause inflammation in the synovium – a layer of soft tissue on the inner surface of joints, eventually leading to rheumatoid arthritis. Rheumatoid factor can also cause other symptoms seen in autoimmune disorders like Sjogren’s Syndrome.

Rheumatoid factor is commonly associated with rheumatoid arthritis because when the antibody was discovered, it was initially mostly used to diagnose rheumatoid arthritis. Approximately 80% of adult rheumatoid arthritis patients test positive for rheumatoid factor. However, people without any autoimmune disorders can also test positive for rheumatoid factor.

What Causes Rheumatoid Factor?

It is not exactly known what causes rheumatoid factor to develop in the blood. However, it is thought to be a combination of genetics and other external risk factors. The uncertainty may be because certain people have low levels of rheumatoid factor, which may not ever be enough to trigger a significant autoimmune response.

On the other hand, people who have high levels of rheumatoid factor may go on to develop autoimmune disorders like rheumatoid arthritis, while others with elevated rheumatoid factor may not develop an autoimmune disorder. It isn’t completely known what triggers the autoimmune response that causes rheumatoid arthritis.

How to Test for Rheumatoid Factor

Testing for rheumatoid factor is done through a blood test. The blood is drawn then analyzed for the presence of this particular protein. If the results show a certain level of rheumatoid factor, then the test is said to be positive. Rheumatoid factor tests can also detect lower levels of rheumatoid factor, but the test result is not considered positive unless it crosses that threshold.

What Do Rheumatoid Factor Test Results Mean?

Testing positive for rheumatoid does not necessarily mean the patient has rheumatoid arthritis. A positive for rheumatoid factor test results means that it can lead to or is the cause of inflammatory symptoms from an autoimmune disorder.

In certain cases, however, patients may test positive for rheumatoid factor, yet remain healthy and never experience any obvious symptoms.

Rheumatoid factor can be present in patients several months or even years before clinical rheumatoid arthritis symptoms develop. Depending on the level of symptoms a patient exhibits, the rheumatoid factor test results can assist doctors in reaching a rheumatoid arthritis diagnosis.

Positive rheumatoid factor results in someone who has been clinically diagnosed with rheumatoid arthritis may also indicate the potential for a more aggressive disease course. This is possible in both children and adult patients.

Patients who test negative for rheumatoid factor but still exhibit symptoms and meet other diagnostic criteria may still be diagnosed with rheumatoid arthritis.

Diagnosing Rheumatoid Arthritis with the Rheumatoid Factor Test

Patients who test positive for rheumatoid factor aren’t necessarily diagnosed with rheumatoid arthritis right away. There must also be a clear history of consistent rheumatoid arthritis symptoms.

If your doctor suspects symptoms of rheumatoid arthritis, other criteria must first be taken into consideration before reaching a diagnosis. The presence of rheumatoid factor alone does not typically lead to an immediate rheumatoid arthritis diagnosis. Doctors look at physical symptoms, medical history and may conduct other blood tests, like anti-CCP, as well as imaging scans to help identify the condition.

Depending on the final diagnosis, in some cases the presence of rheumatoid factor in a patient’s blood may help determine the type of treatment that will be provided to that patient, such as disease-modifying antirheumatic drugs (DMARDs).

A positive rheumatoid factor test along with a rheumatoid arthritis diagnosis can potentially help the doctor determine a prognosis and an appropriate course of treatment. This may depend on a variety of factors.

How Rheumatoid Factor Affects Prognosis

Determining a prognosis for rheumatoid arthritis patients can be a complicated process. The disease affects different people in different ways. A prognosis can depend largely on the type and severity of symptoms the patient displays, as well as their medical history.

Many doctors and researchers feel that a positive rheumatoid factor test result may predict a more severe pattern of symptoms and overall disease course. Extra-articular symptoms like rheumatoid nodules may be more likely to form in patients who have positive rheumatoid factor blood test results. Other aggressive symptoms, though rare, could be more likely to occur in rheumatoid factor positive patients. These may include symptoms due to an autoimmune effect on the lung and heart.

Rheumatoid factor-positive patients may also have a higher disease activity score, meaning frequent flare-ups and fewer remission periods.

Keep in mind this isn’t always the case. If rheumatoid factor is tested and symptoms are detected early, a diagnosis can be quickly reached. Early diagnosis means treatment can begin sooner, hence preventing further progression of joint damage, swelling and pain.

Rheumatoid Factor

Rheumatoid factor is an antibody your immune system makes. But, unlike other antibodies, it doesn’t fight germs and infections. Instead, it can damage healthy tissue in your body. Providers test for it using a blood test. A rheumatoid factor test can help providers diagnose certain autoimmune diseases, especially rheumatoid arthritis.

Overview

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.

Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

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:

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

Test Details

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.

Results and Follow-Up

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 (

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.