Rheumatoid Factor
Rheumatoid Factor (RF)
What this test measures
Rheumatoid factor is an antibody found in many people with rheumatoid arthritis. However, it can also be present in other conditions and in some healthy people.
Understanding the numbers
Typical range: Less than 14 IU/mL (negative)
A positive result doesn't always mean rheumatoid arthritis. About 20% of RA patients are RF negative, and some healthy people are RF positive.
- Negative: 0–14 IU/mL
- Weak positive: 14–50 IU/mL
- Positive: 50–100 IU/mL
- Strong positive: 100–200 IU/mL
Key numbers
- 14 IU/mL — Cut-off (varies by lab)
Cut-off varies by laboratory. RF is one part of the diagnostic picture — it can be positive in Sjögren's, SLE, hepatitis C, infections and in 5-10% of healthy people. Anti-CCP (cyclic citrullinated peptide) is more specific for rheumatoid arthritis and is usually checked alongside.
Ranges can vary slightly between laboratories — your report may show slightly different numbers. This page does not read or interpret your result; your GP looks at it alongside your history and other tests.
What a positive or higher-than-normal result can mean
- May support a diagnosis of rheumatoid arthritis if you have symptoms
- Higher levels are more strongly associated with RA
- Can also be positive in other autoimmune conditions
- Some infections and liver disease can cause positive RF
Questions you could ask your GP
- Does this result mean I have rheumatoid arthritis?
- Do I need other tests like anti-CCP antibodies?
- Should I be referred to a rheumatologist?
- What treatment options are available?
Example stories
These are made-up examples to show how results are talked about in real appointments. They are not real patients.
Classic RA — high RF and CCP
Priyanka had hot swollen small joints in her hands and feet for three months with morning stiffness over an hour. RF 180, anti-CCP strongly positive, CRP 45.
What the GP said: “The joint pattern, morning stiffness, raised inflammatory markers, and strongly positive RF and CCP make rheumatoid arthritis very likely. I'm referring urgently to rheumatology — early treatment makes a big difference to long-term outcomes.”
What happened next: Rheumatology started methotrexate within 4 weeks; her joints settled and she went into low disease activity.
Strongly positive RF plus anti-CCP, with the right clinical picture, supports rheumatoid arthritis. Early disease-modifying treatment (within 3 months of symptoms) significantly improves long-term outcomes.
Weakly positive RF — no disease
Tony's RF was 28 IU/mL on a screen for vague aches. No joint swelling, normal CRP. Anti-CCP was negative.
What the GP said: “A weakly positive RF in an older adult with no joint swelling and normal inflammatory markers usually doesn't mean rheumatoid. Anti-CCP is negative, which makes it even less likely. We'll review if any joint swelling appears.”
RF becomes increasingly common in older healthy adults — up to 10% can be weakly positive. Without inflammatory features, CCP negative, and normal bloods, it's usually background noise.
Sjögren's syndrome — RF positive
Victoria had dry eyes, dry mouth, and fatigue. RF 95, ANA positive, anti-Ro positive, anti-CCP negative.
What the GP said: “This pattern — dry symptoms with positive RF, ANA, and anti-Ro — is Sjögren's syndrome. You don't have joint swelling so rheumatoid isn't the picture. I'll refer to rheumatology and organise symptomatic treatment for dry eyes/mouth.”
What happened next: Rheumatology confirmed Sjögren's; artificial tears, pilocarpine, and vigilant dental care improved symptoms.
RF can be positive in several autoimmune conditions — not only rheumatoid. Sjögren's syndrome classically gives dry eyes and mouth with positive RF, ANA, and specifically anti-Ro.
Seronegative RA — RF negative but disease present
Radhika had classic symmetrical small joint swelling and morning stiffness. RF 9 (negative), anti-CCP 85 (positive), CRP 35.
What the GP said: “About one in five people with rheumatoid arthritis have negative RF. Your anti-CCP is positive and your joints clearly look rheumatoid. I'm referring you urgently.”
What happened next: Early treatment achieved remission within a year.
A negative RF doesn't exclude rheumatoid arthritis — around 20% are RF-negative. Anti-CCP is more specific and picks up many of these. Clinical examination remains the most important part of the picture.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.