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Rheumatoid Factor (RF) Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Rheumatoid Factor (RF) Test

A rheumatoid factor (RF) test measures the level of a specific protein in your blood to help diagnose autoimmune disorders like rheumatoid arthritis.

What is a rheumatoid factor (RF) test?

A rheumatoid factor (RF) test checks a sample of your blood for rheumatoid factor, a protein made by the immune system. Normally, your immune system produces antibodies to attack germs. However, rheumatoid factor is an antibody that mistakenly attacks healthy cells, usually immunoglobulin G (IgG). This can occur when the immune system is overactive or malfunctioning.

While many healthy people have small amounts of RF in their blood, higher levels—especially when accompanied by specific symptoms—may indicate an autoimmune disorder or other health conditions.

What is it used for?

RF testing is primarily used alongside other diagnostic tools to identify rheumatoid arthritis (RA), a chronic autoimmune disorder that causes joint pain, swelling, and stiffness. It may also be used to investigate other autoimmune conditions, certain infections, and specific types of cancer.

Why do I need an RF test?

Your provider may order this test if you exhibit symptoms of rheumatoid arthritis, including:

  • Joint pain or stiffness, particularly in the morning or after inactivity.
  • Joint tenderness, redness, and warmth.
  • Joint swelling that interferes with daily activities like buttoning clothes or bending knees.
  • Fatigue, fever, and loss of appetite.
  • Rheumatoid nodules (hard bumps under the skin near joints).

Testing may also be indicated to check for other conditions associated with high RF levels, such as:

  • Autoimmune disorders: Sjögren syndrome, lupus, scleroderma, or juvenile idiopathic arthritis.
  • Chronic infections: Hepatitis C, tuberculosis, or endocarditis.
  • Certain cancers: Including leukemia.

What happens during an RF test?

A healthcare professional will collect a blood sample from a vein in your arm using a small needle. The process typically takes less than five minutes. At-home test kits are also available, which involve pricking your finger to collect a sample for laboratory analysis; if you use an at-home kit, ensure you share the results with your provider.

What do the results mean?

RF test results are generally reported as positive or negative, though they cannot diagnose a condition on their own.

  • Negative (normal) result: Little to no rheumatoid factor is present. This does not definitively rule out rheumatoid arthritis, as some people with the condition have low or normal RF levels.
  • Positive (abnormal) result: Higher levels of RF were found. Your provider will interpret this in the context of your medical history and other test results to determine if you have an autoimmune disease, chronic infection, or cancer.

Note: An RF test is not used to diagnose osteoarthritis, as that condition is not autoimmune and does not involve rheumatoid factor.

Frequently Asked Questions

Results are usually available within a few days to a week, depending on the laboratory. "High" levels indicate a higher concentration of rheumatoid factor in your blood. While high levels are often associated with active rheumatoid arthritis or other autoimmune conditions, they are not diagnostic on their own. Mildly elevated levels can be seen in healthy older adults or those with chronic infections like Hepatitis C. Your provider will interpret the level in the context of your symptoms and other test results.
Yes, acute infections, including viral illnesses, can sometimes cause a temporary rise in rheumatoid factor levels. This is because the immune system is activated during an infection, which can lead to the production of various antibodies, including RF. If you are tested during or shortly after an acute illness, your provider may recommend repeating the test after you have recovered to ensure the levels have returned to baseline before making a final diagnosis.
Yes, a significant portion of people with rheumatoid arthritis are "seronegative," meaning they test negative for rheumatoid factor. A negative RF test does not rule out RA, especially if you have classic symptoms like symmetric joint swelling and morning stiffness lasting more than 30 minutes. Your provider will likely order additional tests, such as anti-CCP (anti-cyclic citrullinated peptide) antibodies, which are more specific for RA, and use imaging or clinical evaluation to make a diagnosis.
No special preparation, such as fasting or stopping medications, is typically required for an RF test. You can eat and drink normally before the appointment. However, you should inform your healthcare provider if you are taking any medications or supplements, as some drugs can potentially influence immune markers, though this is less common with RF than with other tests. If you have a history of fainting during blood draws, let the phlebotomist know so they can take precautions.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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