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Rheumatoid Factor (Immunoassay) - Serum

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

This test measures the presence of antibodies in your blood that may indicate rheumatoid arthritis or other autoimmune conditions.

Quick summary

["Rheumatoid factor can help doctors assess potential autoimmune diseases."]

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

Key facts at a glance

LOINC
5298-5
Short code
Rheumatoid fact Ser Ql Shp Aggl
Synonyms
Rheumatoid fact Ser Ql 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

What Is Rheumatoid Factor?

Rheumatoid factor (RF) is an antibody found in the blood that can target your own healthy cells, contributing to inflammation in joints and other tissues. While it can be present in people without symptoms, it is often elevated in those with rheumatoid arthritis or other autoimmune disorders like lupus or Sjogren’s syndrome.

Why Might You Need This Test?

Your doctor may order this test to help diagnose or monitor conditions like rheumatoid arthritis, especially when other symptoms (such as joint pain, swelling, or stiffness) are present. It can also be used as part of a broader evaluation for autoimmune diseases.

How Is the Test Performed?

A blood sample is drawn from a vein in your arm. The serum portion of your blood is then tested for the presence of rheumatoid factor antibodies using an immunoassay method, which detects specific antibodies in your blood.

What Do Results Mean?

Results are not always definitive on their own. High levels of rheumatoid factor may suggest an increased risk of autoimmune diseases, but they do not always correlate directly with disease activity. Your doctor will consider your symptoms, medical history, and other test results to interpret the results accurately.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Rheumatoid Factor (RF)

Frequently asked questions

How often will I need this test?
Rheumatoid factor testing is often done as part of an initial evaluation for autoimmune diseases or during follow-up visits to monitor disease progression. Frequency depends on your symptoms, treatment plan, and doctor’s recommendations. Some people may need it yearly or more often if their condition is active.
What are the possible side effects of this test?
The most common side effect is a mild bruise, redness, or soreness at the needle insertion site. Rarely, a small amount of bleeding or swelling may occur. Most side effects are minor and resolve quickly.
Can I eat or drink before this test?
You can usually eat and drink normally before this test unless your doctor specifies otherwise. For some tests, fasting may be required, but rheumatoid factor testing does not typically require dietary restrictions.
  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