###1: Rheumatoid Factor IgM Concentration, Serum
###3: This blood test measures the amount of IgM rheumatoid factor antibodies in serum. These antibodies can be associated with rheumatoid arthritis and several other conditions.
["###4: A positive or elevated IgM rheumatoid factor result can support an autoimmune evaluation, but it cannot diagnose rheumatoid arthritis by itself."]
Key facts at a glance
- LOINC
- 11573-3
- Short code
- RF IgM Ser-aCnc
- Synonyms
- RF IgM Ser-aCnc
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 86430
- 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
###5: What the test measures
###6: Rheumatoid factor is an antibody that can recognize part of another antibody, usually IgG. This test specifically measures the IgM form of rheumatoid factor in a serum sample.
###7: How to interpret the result
###8: A positive or elevated result means IgM rheumatoid factor is present in the blood. This finding is more common in rheumatoid arthritis but may also occur with other autoimmune diseases, chronic infections, liver disease, certain cancers, or in some older adults.
###9: How the test is performed
###10: A healthcare professional draws blood and separates the serum for laboratory analysis. The results are reported as positive or negative, or with a concentration or titer depending on the laboratory method. Fasting is generally not required unless the ordering clinician gives specific instructions.
###11: Why the result matters
###12: The result can help a clinician evaluate persistent joint pain, swelling, or stiffness. Results are interpreted with symptoms, physical findings, and other tests such as anti-CCP antibodies; a rheumatologist may be consulted when the findings are concerning.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
###13: Clinical significance: IgM rheumatoid factor is useful as one marker in the evaluation of suspected rheumatoid arthritis, particularly when symptoms have been present for some time. However, it is not specific enough to establish the diagnosis on its own, and a positive result does not necessarily mean that rheumatoid arthritis is present or that treatment is needed.
Short name
###2: IgM rheumatoid factor (IgM RF)
Frequently asked questions
###14: Does a positive result mean I have rheumatoid arthritis?
###16: Can someone with rheumatoid arthritis have a negative result?
###18: Do I need to fast before this test?
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