Skip to content

Rheumatoid Factor (IgM) by Immunoassay (serum/plasma)

Published: August 9, 2026Updated: August 16, 2026

This test measures the presence of rheumatoid factor, an antibody found in the blood that may indicate rheumatoid arthritis or other autoimmune conditions.

Quick summary

["RF tests help identify potential autoimmune diseases like rheumatoid arthritis."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
17534-9
Short code
Rheumatoid fact Fld IA-aCnc
Synonyms
Rheumatoid fact Fld IA-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ia
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

What Is Rheumatoid Factor?

Rheumatoid factor (RF) is an antibody that your immune system produces in response to certain proteins in your body. While it can be found in some people without illness, high levels may signal an autoimmune condition like rheumatoid arthritis, where the body attacks its own tissues.

Why Might You Need This Test?

Doctors may order this test if you have symptoms like joint pain, swelling, or stiffness—common in rheumatoid arthritis. It can also be used as part of a broader evaluation for autoimmune diseases or to monitor disease activity in patients already diagnosed.

How Is the Test Performed?

A blood sample is drawn from a vein, usually in your arm. The sample is sent to a lab where it is tested using an immunoassay method to detect rheumatoid factor antibodies.

What Do Results Mean?

Results are not always definitive on their own. Positive results (indicating the presence of RF) may suggest an increased risk of autoimmune conditions, but they do not confirm a diagnosis. Doctors will consider your symptoms, medical history, and other test results before making a conclusion.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Rheumatoid Factor (RF) Test

Frequently asked questions

Why is rheumatoid factor tested?
Rheumatoid factor is often tested to help diagnose or monitor rheumatoid arthritis or other autoimmune diseases. While it can be a useful marker, it is not specific to any one condition and may be found in other health issues or even in healthy individuals.
Can rheumatoid factor levels change over time?
Yes, rheumatoid factor levels can fluctuate. They may rise during active disease phases and sometimes decrease with treatment or disease remission. Regular monitoring may be needed to track changes.
Is this test always accurate?
No, test accuracy depends on proper sample handling, lab techniques, and interpretation by healthcare providers. False positives or negatives can occur, so results should be reviewed in the context of your overall health and symptoms.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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