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Rheumatoid Factor (Serum/Plasma)

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

This test measures the presence of antibodies called rheumatoid factor in your blood, which may indicate an autoimmune condition like rheumatoid arthritis.

Quick summary

["Rheumatoid factor can help diagnose or monitor certain autoimmune diseases."]

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

Key facts at a glance

LOINC
13191-2
Short code
Deprecated Rheumatoid fact SerPl-aCnc
Synonyms
Deprecated Rheumatoid fact SerPl-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 some people with autoimmune diseases. Normally, your immune system protects your body from infections. In rheumatoid arthritis and other autoimmune conditions, the immune system mistakenly attacks healthy tissues, and RF may play a role in this process. This test checks for elevated levels of RF in your blood.

Why Might You Need This Test?

Doctors may order this test if you have symptoms of rheumatoid arthritis, such as joint pain, swelling, or stiffness, or if you have other autoimmune conditions. It can also be used to monitor disease activity or response to treatment.

What Does a Positive Result Mean?

A positive RF test means your body is producing these antibodies, which may suggest an increased risk of autoimmune diseases like rheumatoid arthritis. However, not everyone with a positive RF has rheumatoid arthritis, and some people with the condition may test negative.

How Is the Test Done?

A blood sample is taken from a vein in your arm. The blood is then sent to a lab for testing using an immunoassay method, which detects the presence of rheumatoid factor antibodies.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

RF (Serum/Plasma)

Frequently asked questions

What Are Common Causes of False Positives?
False positives can occur due to other conditions, such as infections (like hepatitis or HIV), certain medications, or aging. If your test is positive, your doctor may recommend further testing to confirm or rule out rheumatoid arthritis.
How Often Should I Get This Test?
Your doctor will determine the frequency based on your symptoms, medical history, and treatment plan. Regular monitoring may be needed if you have an autoimmune condition.
Can This Test Be Used to Predict Disease Progression?
While RF can help identify potential autoimmune activity, it is not a definitive predictor of disease progression. Doctors use it alongside other tests and clinical findings to make assessments.
  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