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Rheumatoid factor
Definition
RF is an antibody that attaches to a substance in the body called immunoglobulin G (IgG), forming a molecule known as an immune complex. The immune complex can trigger different types of inflammation-related
processes in the body.
This article discusses the test to detect and measure the level of RF in the blood.
Alternative Names
RF
How the Test is Performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic
band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test
strip. A bandage may be placed over the area if there is any bleeding.
How to Prepare for the Test
No special preparation is usually necessary.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
This test is most often used to diagnose rheumatoid arthritis. About 80% of patients with rheumatoid arthritis have positive RF tests.
It may also be used to rule out or diagnose other inflammation-related conditions.
Normal Results
Normal values depend on what method the laboratory uses to detect and measure the RF. Some examples are below:
• Less than 60 u/mL (with the nephelometric method)
• Less than 1:80 titer (with the agglutination method)
What Abnormal Results Mean
A positive test may be due to:
• Chronic hepatitis
• Chronic viral infection
• Dermatomyositis
• Infectious mononucleosis
• Leukemia
• Rheumatoid arthritis
• Scleroderma
• Systemic lupus erythematosus
Additional conditions under which the test may be performed:
• Adult Still's disease
• Juvenile rheumatoid arthritis
• Nephrotic syndrome
• Sjogren syndrome
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks:
• Excessive bleeding
• Fainting or feeling lightheaded
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
Considerations
The RF test can be positive in some healthy people.
Reviewed By: Steve Lee, DO, Rheumatology Fellow, Loma Linda University Medical Center, Loma Linda, CA. Review provided by VeriMed Healthcare Network.
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