Lab result explainedInflammationLast updated November 10, 2026

Rheumatoid factor test: normal range and what a high or positive RF means

Rheumatoid factor (RF) · Rheumatoid factor (often ordered with anti-CCP, ESR and CRP) · reported in IU/mL (nephelometry or turbidimetry); some labs report a titer (1:20, 1:40, 1:80, 1:160) from latex agglutination

Rheumatoid factor (RF) is an antibody, usually of the IgM class, that binds to the tail end of your own IgG antibodies, and the rheumatoid factor test measures how much of it is in your blood. It was the first autoantibody linked to rheumatoid arthritis and still carries the disease's name, but it is not specific to it. Most US laboratories call a result under about 14 to 20 IU/mL negative; a result above that is positive, and the higher it is, the more likely it reflects rheumatoid arthritis or another autoimmune disease rather than chance.

About 70 to 80 percent of people with rheumatoid arthritis have a positive RF, which means 20 to 30 percent (seronegative RA) do not, and a negative test never rules the disease out. In the other direction, RF is positive in around 5 percent of healthy adults, rising to 10 to 25 percent over the age of 70, and in most people with Sjögren's syndrome, cryoglobulinemia and chronic hepatitis C, plus a long list of infections and inflammatory conditions. A positive RF in someone with no joint symptoms is therefore common and usually not rheumatoid arthritis.

RF is now read together with anti-CCP (anti-citrullinated protein) antibodies, which are about as sensitive for rheumatoid arthritis but far more specific. The 2010 ACR/EULAR classification criteria score both: a low-positive result (up to three times the upper limit of normal) earns 2 points and a high-positive result (above three times the limit) earns 3, alongside joint counts, inflammatory markers and symptom duration. A high RF with a high anti-CCP, swollen joints and a raised CRP is rheumatoid arthritis; a low RF alone is a prompt for questions, not a diagnosis.

RF at a glance

What it is: an autoantibody (mainly IgM) directed against the Fc portion of your own IgG, measured by nephelometry or turbidimetry in IU/mL, or by latex agglutination as a titer.
Normal: below about 14 IU/mL at many labs; others use 15, 20 or 30 IU/mL, or a titer below 1:20 to 1:40. Labs differ, so use the cut-off on your report.
Low positive: up to 3 times the upper limit (roughly 15 to 45 IU/mL); high positive: above 3 times the limit (above about 45 IU/mL). High titers are much more likely to mean rheumatoid arthritis and predict more erosive disease.
Positive in 70 to 80 percent of people with rheumatoid arthritis, 75 to 95 percent with Sjögren's, most with hepatitis C-related cryoglobulinemia, and 5 percent of healthy adults (up to a quarter of healthy people over 70).
A negative RF does not exclude rheumatoid arthritis; 20 to 30 percent of cases are seronegative.
Next step: anti-CCP antibodies, ESR and CRP, a CBC, and if you have joint pain and swelling for more than 6 weeks, an early rheumatology referral; hepatitis C testing if the RF is high with no joint disease.

Have your whole report? Paste it into the free Lab Explainer

Every marker explained in plain language, in context with the others, with questions to bring to your appointment. No account needed.

What RF measures

Rheumatoid factors are antibodies that recognize the constant (Fc) region of IgG, the most abundant antibody class. Small amounts are a normal part of immune regulation, helping to clear immune complexes, and they rise briefly after infections and vaccinations. In rheumatoid arthritis and some other diseases, B cells in inflamed tissue produce RF persistently and at high levels; in the joint, RF binds IgG to form immune complexes that activate complement and recruit inflammatory cells, so high-titer RF is associated with more joint erosions, rheumatoid nodules, lung disease and vasculitis.

Most laboratories now measure IgM RF quantitatively by nephelometry or turbidimetry: your serum is mixed with IgG-coated latex particles, and the degree of clumping is read optically and converted to international units against a WHO reference preparation. Older latex agglutination tests report a titer (the highest dilution of serum that still clumps the particles, such as 1:40 or 1:160). ELISA methods can also measure IgG and IgA RF, which are not routinely needed but may be positive in some seronegative patients. Results between methods are not interchangeable, and the reference range printed on your report is the one that applies.

Because RF rises with ordinary immune activity, timing matters. A recent viral illness, vaccination or active infection can produce a transient low-positive result, and conditions that stimulate B cells over long periods (chronic hepatitis C, endocarditis, tuberculosis, chronic liver disease) produce persistent ones. RF has no daily rhythm and does not require fasting, but it is best measured when you are well and, ideally, before treatment with drugs such as rituximab, which lowers it.

Normal range for RF

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (IU/mL (nephelometry or turbidimetry); some labs report a titer (1:20, 1:40, 1:80, 1:160) from latex agglutination)	Notes
Negative	Below about 14 IU/mL	Many labs use 15, 20 or 30 IU/mL as the cut-off, or a latex titer below 1:20 to 1:40. Use the reference range printed on your report.
Low positive	Above the cut-off up to 3 times the upper limit (about 15–45 IU/mL)	Scores 2 points in the 2010 ACR/EULAR rheumatoid arthritis criteria. Common in healthy older people, after infections and in many other conditions.
High positive	Above 3 times the upper limit (above about 45 IU/mL)	Scores 3 points. Much more likely to indicate rheumatoid arthritis, Sjögren's or cryoglobulinemia; associated with more erosive and extra-articular disease.
Very high	Above 100 IU/mL	In a Danish population study, people with RF above 100 IU/mL had a 26-fold higher risk of developing rheumatoid arthritis over the following 10 years than those under 25 IU/mL.
Latex titer	Below 1:20 negative; 1:40 to 1:80 low positive; 1:160 and above high positive	Titers and IU/mL cannot be converted exactly between labs.
Healthy adults	About 5 percent positive, usually low titer	Rises with age: 10 to 25 percent of healthy people over 70 have a low-positive RF.
Rheumatoid arthritis	70 to 80 percent positive; about 50 percent in the first months of disease	RF can appear up to 10 years before symptoms. 20 to 30 percent of patients remain seronegative.
Sjögren's syndrome and hepatitis C cryoglobulinemia	Often strongly positive (frequently above 100 IU/mL)	These are the main alternative explanations for a high RF without joint swelling.

High (positive) rheumatoid factor

A positive rheumatoid factor means your immune system is making antibodies against your own IgG at a level above the laboratory's cut-off. What it means for you depends mostly on the level and on your symptoms. A high-positive result, above three times the upper limit of normal, in someone with pain, stiffness and swelling in the small joints of the hands and feet that lasts more than an hour each morning, is strong evidence of rheumatoid arthritis, particularly if anti-CCP is also positive and CRP or ESR is raised. In that setting the diagnosis is usually made clinically and treatment with disease-modifying drugs is started early, because erosions develop within the first two years and seropositive disease tends to be more aggressive.

A low-positive result (just above the cut-off) in someone with no joint symptoms is a different situation and is the one most people searching this page are in. It is found in about 5 percent of the general population and a quarter of healthy people over 70, after many viral infections, and in a range of chronic conditions. The positive predictive value of a low-positive RF for rheumatoid arthritis in the general population is well under 10 percent. The usual advice is an anti-CCP test (if that is negative, rheumatoid arthritis becomes less likely still), a check of the clinical picture for Sjögren's symptoms, liver disease or hepatitis C, and a review if joint symptoms develop.

Three things RF does not do are worth knowing. It does not reliably track disease activity, so repeating it to see whether treatment is working is of limited use, though titers often fall on effective therapy and rituximab in particular lowers it. It does not diagnose rheumatoid arthritis on its own; the 2010 criteria require at least one definitely swollen joint. And it does not rule out other causes of joint pain: osteoarthritis, gout, psoriatic arthritis, viral arthritis and fibromyalgia can all coexist with an incidental positive RF.

Common causes

Rheumatoid arthritis
Positive in 70 to 80 percent of established cases and about half of early cases. High titers (above 3 times the upper limit or above 50 IU/mL) are associated with erosions, rheumatoid nodules, interstitial lung disease and vasculitis. RF can precede joint symptoms by years.
Sjögren's syndrome
RF is positive in 75 to 95 percent of people with primary Sjögren's, often at high titer, alongside a positive ANA and anti-Ro/SSA antibodies. Dry eyes, dry mouth, parotid swelling and fatigue are the clues; joint pain is common but erosions are not.
Chronic hepatitis C and mixed cryoglobulinemia
Hepatitis C stimulates B cells to produce RF in 70 percent or more of chronically infected people, and in cryoglobulinemia the RF is part of the cryoglobulin itself, producing very high titers with purpura, neuropathy and kidney disease. A high RF without joint swelling should prompt hepatitis C testing.
Healthy aging
Low-titer RF is present in about 5 percent of adults and in 10 to 25 percent of people over 70 without any disease, reflecting age-related changes in B-cell regulation.
Other autoimmune diseases
Systemic lupus (15 to 35 percent), systemic sclerosis (20 to 30 percent), mixed connective tissue disease, dermatomyositis, primary biliary cholangitis and autoimmune hepatitis all produce RF, usually at low to moderate titer.
Chronic infections
Bacterial endocarditis (RF positive in about 40 percent), tuberculosis, syphilis, leprosy, brucellosis, hepatitis B, HIV, EBV, parvovirus and parasitic infections such as malaria and schistosomiasis. The RF usually falls when the infection is treated.
Recent viral infection or vaccination
A transient low-positive RF is common for weeks after influenza, EBV, COVID-19 and other viral illnesses, and occasionally after vaccination. Repeat the test 2 to 3 months later if there are no symptoms.
Chronic lung and liver disease
Idiopathic pulmonary fibrosis, sarcoidosis, silicosis, asbestosis, cirrhosis and chronic alcohol-related liver disease are associated with low-positive RF in 10 to 50 percent of patients.
Blood disorders and cancers
Waldenström's macroglobulinemia (the monoclonal IgM may itself be an RF), lymphoma, leukemia and multiple myeloma, and after chemotherapy or radiation.
Interstitial lung disease, smoking and periodontitis
Smokers have higher rates of RF positivity than non-smokers, and chronic periodontal infection with Porphyromonas gingivalis is linked to both RF and anti-CCP production through citrullination of proteins in the gums.

Symptoms that can go with it

Often none; a low-positive RF in a person without joint symptoms usually causes nothing
Pain, swelling and warmth in the knuckles, finger joints, wrists, balls of the feet or toes, typically symmetrical
Morning stiffness lasting more than an hour, easing with movement
Fatigue, low-grade fever and loss of appetite in active inflammatory arthritis
Firm lumps (rheumatoid nodules) over the elbows or finger joints
Dry, gritty eyes and dry mouth (Sjögren's), or swollen salivary glands
Purple spots on the lower legs, numbness or tingling in the feet, or foamy urine with cryoglobulinemia
Breathlessness or a dry cough, which can indicate rheumatoid lung disease

Read it alongside

Anti-CCP antibodies — similar sensitivity to RF for rheumatoid arthritis but about 95 percent specific; both positive at high titer makes the diagnosis very likely and predicts erosive disease.
CRP and ESR — measure the inflammation itself; a high RF with normal CRP and ESR and no swollen joints is less likely to be active rheumatoid arthritis.
Complete blood count — anemia of chronic disease and a raised platelet count accompany active inflammation; a low white count with a high RF and splenomegaly suggests Felty's syndrome.
ANA and ENA panel — positive ANA with anti-Ro/SSA and a high RF points to Sjögren's syndrome or lupus rather than rheumatoid arthritis.
Hepatitis C antibody — the most important non-rheumatological cause of a strongly positive RF; cryoglobulins are checked if purpura, neuropathy or kidney involvement are present.
Liver enzymes (ALT, AST, ALP) — chronic liver disease raises RF and needs to be known before methotrexate or other treatment is started.
Uric acid — gout is a common mimic of rheumatoid arthritis and can coexist with an incidental positive RF.
X-rays or ultrasound of hands and feet — look for erosions and synovitis; ultrasound can detect inflammation in joints that are painful but not visibly swollen.

What usually happens next

If RF is positive and you have joint pain, swelling or morning stiffness lasting more than 6 weeks, ask for anti-CCP, CRP, ESR, a CBC and an early rheumatology referral; starting disease-modifying treatment within the first 3 to 6 months of rheumatoid arthritis gives the best long-term outcome.
If RF is low-positive and you have no joint symptoms, an anti-CCP test clarifies the risk: a negative anti-CCP makes rheumatoid arthritis unlikely, while a positive one means closer follow-up even without symptoms.
If RF is high (above 3 times the limit, or above 50 to 100 IU/mL) with no joint disease, expect tests for hepatitis C, Sjögren's (ANA, anti-Ro/SSA, dry-eye assessment) and, where there is a rash or neuropathy, cryoglobulins.
A low-positive result after a recent infection or vaccination is usually repeated after 2 to 3 months; a transient RF disappears, a persistent one is noted.
Do not expect RF to be repeated routinely to monitor treatment; disease activity is tracked with joint counts, CRP, ESR and function, though a falling RF on treatment is reassuring.
Keep a note of the result: a positive RF years before symptoms is useful history if joint problems ever develop, and it alerts your clinicians to look for Sjögren's and lung involvement.

Diet, lifestyle and natural levers with evidence

What can move RF once the cause is known. Nothing here replaces finding the cause.

Stop smoking

Strong evidence

Smoking is the strongest environmental risk factor for seropositive rheumatoid arthritis: a meta-analysis of 16 studies found current smokers had about twice the risk of RF-positive RA (and men more than women), with risk climbing with pack-years. In people with the HLA-DRB1 shared epitope, smoking multiplies the risk of antibody-positive disease more than 20-fold. Risk falls back toward that of never-smokers over 15 to 20 years after quitting, and smokers with established RA respond less well to methotrexate and TNF inhibitors.

Treat gum disease

Moderate evidence

Periodontitis is about twice as common in people with rheumatoid arthritis, and the gum bacterium Porphyromonas gingivalis is the only known microbe that citrullinates proteins, the process that generates the targets of anti-CCP antibodies. Small randomised trials found that non-surgical periodontal treatment (scaling and root planing) reduced disease activity scores (DAS28) by about 0.5 to 1 point and lowered ESR in people with RA over 6 to 12 weeks; effects on RF titer were inconsistent.

Omega-3 fish oil at anti-inflammatory doses

Moderate evidence

A meta-analysis of 17 randomised trials found that 2.7 g or more a day of EPA plus DHA for at least 3 months reduced tender joint counts, morning stiffness and NSAID use in rheumatoid arthritis. In a trial of 140 people with early RA treated with standard drugs, those randomised to high-dose fish oil (5.5 g a day) were twice as likely to reach remission and far less likely to need treatment escalation at one year. Fish oil treats the inflammation; it has not been shown to change RF levels.

Doses above 3 g a day increase bleeding tendency with anticoagulants and antiplatelet drugs; discuss before combining.

Mediterranean-style diet

Moderate evidence

In a 12-week randomised trial of 51 people with established rheumatoid arthritis, a Mediterranean diet reduced the DAS28 activity score by 0.56 points, improved physical function and lowered CRP compared with a usual Western diet. Observational studies link higher fish and olive oil intake with lower RA risk and sugar-sweetened drinks with higher risk. The effect is on inflammation and symptoms rather than the RF titer itself.

Regular exercise and weight management

Moderate evidence

Meta-analyses of exercise trials in rheumatoid arthritis show improvements in pain, function, cardiovascular fitness and fatigue without worsening joint damage; both aerobic and resistance training work, with 2 to 3 sessions a week over 12 or more weeks the typical dose. Obesity is associated with higher disease activity scores and a lower chance of remission, and weight loss of 5 to 10 percent improves activity measures in people who are overweight.

Curcumin

Preliminary evidence

In a pilot randomised trial of 45 people with active rheumatoid arthritis, 500 mg a day of a bioavailable curcumin formulation for 8 weeks improved DAS28 scores and tender and swollen joint counts at least as much as diclofenac 50 mg, and meta-analyses of small trials report reductions in ESR and CRP. Trials are short and small, no study has shown a change in RF, and curcumin is an addition to, not a replacement for, disease-modifying treatment.

Increases bleeding risk with anticoagulants and can interact with some chemotherapy; rare reports of liver injury with high-dose products.

When to see a clinician promptly

A single hot, red, swollen joint with fever: septic arthritis is a medical emergency and needs same-day joint aspiration, whatever the RF result.
Joint pain with swelling or morning stiffness lasting more than 6 weeks, especially in the hands and feet, with a positive RF: early rheumatology referral, because treatment started within months prevents permanent joint damage.
A positive RF with new breathlessness or a dry cough (possible rheumatoid lung disease), or with purple spots on the legs, numbness in the feet or blood or protein in the urine (possible cryoglobulinemic vasculitis).
Sudden severe neck pain, weakness, numbness or trouble walking in someone with long-standing rheumatoid arthritis, which can signal instability at the top of the spine.
A high RF without joint symptoms, to be tested for hepatitis C and Sjögren's syndrome.
Red, painful eyes or sudden visual change with rheumatoid arthritis (scleritis), which needs prompt ophthalmology review.

Frequently asked questions

What is the normal range for rheumatoid factor?

Most US laboratories report a rheumatoid factor under about 14 IU/mL as negative, though cut-offs of 15, 20 and 30 IU/mL are also in use, and labs that use latex agglutination call a titer below 1:20 or 1:40 negative. A result above the cut-off but less than three times the upper limit is a low positive; above three times the limit (roughly above 45 IU/mL) is a high positive, which is the level that counts most in the rheumatoid arthritis criteria.

What does a high rheumatoid factor mean?

A high RF, above about three times the upper limit of normal, means a substantial amount of antibody against your own IgG is circulating. With joint pain and swelling it strongly suggests rheumatoid arthritis and predicts more aggressive disease. Without joint symptoms, the likeliest explanations are Sjögren's syndrome (dry eyes and mouth), chronic hepatitis C with cryoglobulinemia, chronic infections such as endocarditis or tuberculosis, or lymphoproliferative disorders, and those are what your clinician will look for.

I have a positive rheumatoid factor but no symptoms. Should I worry?

Usually not. About 5 percent of healthy adults, and up to a quarter of healthy people over 70, have a low-positive RF, and recent infections and vaccinations produce transient positives. The sensible next step is an anti-CCP test: if it is negative and your joints are normal, your risk of developing rheumatoid arthritis is low and no treatment is needed. If anti-CCP is also positive, or your RF is high (above 50 to 100 IU/mL), the risk is higher and you should know the symptoms to watch for and be reviewed if they appear.

Can you have rheumatoid arthritis with a negative rheumatoid factor?

Yes. Around 20 to 30 percent of people with rheumatoid arthritis are seronegative, meaning both RF and anti-CCP are negative, and in the first months of the disease RF is positive in only about half of patients. Seronegative disease is diagnosed from the pattern of joint involvement, inflammatory markers and imaging, and it tends to be less erosive but is treated the same way. A negative RF should never be used to dismiss persistent joint swelling.

What is the difference between rheumatoid factor and anti-CCP?

Both are autoantibodies used to diagnose rheumatoid arthritis and both are positive in about 70 percent of patients, but anti-CCP is far more specific: around 95 percent of people with a positive anti-CCP have or will develop rheumatoid arthritis, compared with roughly 80 to 85 percent specificity for RF, which is also positive in Sjögren's, hepatitis C, infections and healthy older people. Having both positive at high levels is the strongest serological predictor of erosive disease; anti-CCP is the better test to order after a positive RF.

Does rheumatoid factor go up and down with disease activity?

Only loosely. RF titers often fall when rheumatoid arthritis is well controlled, and rituximab in particular lowers them, but the correlation with day-to-day activity is weak and RF rarely becomes negative. Clinicians monitor rheumatoid arthritis with joint counts, CRP, ESR, patient-reported scores and imaging, not by repeating the RF. A rising RF is not by itself a reason to change treatment.

What infections cause a positive rheumatoid factor?

Chronic hepatitis C is the most important, producing a positive RF in 70 percent or more of infected people and very high titers when cryoglobulinemia develops. Bacterial endocarditis, tuberculosis, syphilis, leprosy, hepatitis B, HIV, EBV (glandular fever), parvovirus B19 and parasitic infections such as malaria and schistosomiasis also raise RF, as do many ordinary viral illnesses for a few weeks. Infection-related RF usually falls once the infection is treated or resolves.

Do I need to fast or stop medication before a rheumatoid factor test?

No fasting is needed and most medications do not affect the result. Rituximab lowers RF, and other immunosuppressants may reduce it somewhat over time, so the test is most informative before treatment starts. It is best not to test within a few weeks of a significant infection or vaccination, both of which can cause a temporary low-positive result that would need repeating.

References

Rheumatoid factor (RF) test. MedlinePlus, US National Library of Medicine (2023)View source
Rheumatoid factor. Mayo Clinic (2024)View source
Aletaha D, Neogi T, Silman AJ, et al.. 2010 rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis and Rheumatism (2010)
Nishimura K, Sugiyama D, Kogata Y, et al.. Meta-analysis: diagnostic accuracy of anti-cyclic citrullinated peptide antibody and rheumatoid factor for rheumatoid arthritis. Annals of Internal Medicine (2007)
Nielsen SF, Bojesen SE, Schnohr P, Nordestgaard BG. Elevated rheumatoid factor and long term risk of rheumatoid arthritis: a population based cohort study. BMJ (2012)
Shmerling RH, Delbanco TL. The rheumatoid factor: an analysis of clinical utility. American Journal of Medicine (1991)
Ingegnoli F, Castelli R, Gualtierotti R. Rheumatoid factors: clinical applications. Disease Markers (2013)
Lane SK, Gravel JW. Clinical utility of common serum rheumatologic tests. American Family Physician (2002)
Rheumatoid arthritis (RA). Merck Manual Professional Version (2024)
Sugiyama D, Nishimura K, Tamaki K, et al.. Impact of smoking as a risk factor for developing rheumatoid arthritis: a meta-analysis of observational studies. Annals of the Rheumatic Diseases (2010)
Sköldstam L, Hagfors L, Johansson G. An experimental study of a Mediterranean diet intervention for patients with rheumatoid arthritis. Annals of the Rheumatic Diseases (2003)
Proudman SM, James MJ, Spargo LD, et al.. Fish oil in recent onset rheumatoid arthritis: a randomised, double-blind controlled trial within algorithm-based drug use. Annals of the Rheumatic Diseases (2015)

Related markers

Related conditions

Evidence guides

Worried about your number?

Ask AskMN what your RF result could mean in the context of your other results, symptoms and medications. Free, unlimited, no account needed.

Ask about my RF

This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.