Rheumatoid Factor (RF) – Serum Immunoglobulin G (IgG) Autoantibody
This test measures the presence of antibodies in your blood that may indicate an autoimmune response, often linked to rheumatoid arthritis or other inflammatory conditions.
["RF tests help doctors assess possible autoimmune diseases like rheumatoid arthritis."]
Key facts at a glance
- LOINC
- 5300-9
- Short code
- Rheumatoid fact Titr Ser Shp Aggl
- Synonyms
- Rheumatoid fact Titr Ser Shp Aggl
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- sheep-cell-aggl
- 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
The rheumatoid factor test measures the level of rheumatoid factor proteins, a type of autoantibody, in your blood. These proteins are produced by your immune system and may attack healthy tissue, and elevated levels are often linked to rheumatoid arthritis and other autoimmune conditions.
The test detects rheumatoid factor, a type of antibody (specifically immunoglobulin G, or IgG) that your immune system produces against its own proteins. This can happen in conditions like rheumatoid arthritis, but it can also occur in other autoimmune diseases or infections.
Your doctor may order this test if you have joint pain, swelling, or morning stiffness lasting more than 30 minutes, along with fatigue or unexplained discomfort in multiple joints, to help determine whether rheumatoid arthritis or another inflammatory condition could be causing your symptoms.
Doctors may order this test to help diagnose or monitor rheumatoid arthritis, lupus, or other inflammatory conditions. It can also be used to check for infections or other autoimmune responses.
In most cases, no special preparation is needed before a rheumatoid factor blood test, and you can usually eat and drink normally. However, be sure to tell your doctor about any medications, supplements, or recent vaccines you have received, since these can occasionally influence your results.
No special preparation is usually needed. You may be asked to fast before the test, but this depends on your doctor’s instructions. Bring any medications you’re currently taking.
A healthcare professional will place an elastic band around your upper arm, clean the skin at the puncture site, and draw a small blood sample from a vein, usually in your arm. The process takes only a few minutes, and the sample is then sent to a laboratory for analysis.
A healthcare professional will draw blood from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause significant discomfort. The blood sample is then sent to a lab for analysis.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance
Short name
Rheumatoid Factor (RF)
Frequently asked questions
Rheumatoid factor is not always specific to rheumatoid arthritis—it can appear in other autoimmune diseases, chronic infections, or even some healthy older adults. While positive results may raise suspicion for autoimmune conditions, they don’t confirm a diagnosis alone. Your doctor will consider symptoms, other test results, and clinical findings for a full assessment.
A positive rheumatoid factor result suggests your immune system may be producing antibodies against its own proteins, which can be linked to conditions like rheumatoid arthritis or other autoimmune diseases. However, it doesn’t definitively diagnose the condition without further evaluation.
Yes, rheumatoid factor levels can fluctuate. They may rise during active disease or infections and sometimes decrease with treatment. Regular monitoring can help track disease progression or response to therapy.
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