Rheumatoid Factor (Quantitative) in Serum or Plasma
This test measures the presence of antibodies that attack healthy joint tissues, often linked to rheumatoid arthritis or other autoimmune conditions.
["RF helps diagnose or monitor autoimmune diseases affecting joints and other body systems."]
Key facts at a glance
- LOINC
- 45156-7
- Short code
- Rheumatoid fact Fld Ql LA
- Synonyms
- Rheumatoid fact Fld Ql LA
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- la
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
Why This Test Matters
Rheumatoid factor (RF) is an antibody that can be found in higher amounts in people with certain autoimmune diseases, such as rheumatoid arthritis. While RF is not always specific to rheumatoid arthritis, it can help doctors assess whether you may have an autoimmune condition affecting your joints, skin, or other organs. This test is often used alongside other tests to guide treatment decisions.
How the Test Works
The test detects the concentration of RF in your blood. It involves drawing blood from a vein in your arm and sending it to a lab for analysis using an immunoassay method, which measures the antibody’s presence and level.
What to Expect Before the Test
No special preparation is needed for this test. You may have a small bruise or sore spot where the needle was inserted, but this usually fades quickly. If you’re on blood-thinning medication, let your doctor know before the test.
What to Expect After the Test
You can return to your normal activities immediately. If you experience unusual bleeding, swelling, or pain at the injection site, contact your healthcare provider. Most people find the procedure quick and not overly uncomfortable.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Elevated RF levels may indicate an autoimmune condition, such as rheumatoid arthritis, but they can also appear in other conditions like lupus, Sjogren’s syndrome, or infections. While RF is not definitive for rheumatoid arthritis, it can support a diagnosis when combined with clinical findings and other tests. Some people with normal RF levels still develop rheumatoid arthritis, so this test is often used as part of a broader evaluation.
Short name
RF (Serum/Plasma)
Frequently asked questions
How long does it take to get my RF test results?
Can RF test results be affected by diet or medications?
Is RF test always positive in rheumatoid arthritis?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy