Rheumatoid factor

This is a test that measures the presence and level of rheumatoid factor (RF) in the blood.

RF

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child:

The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

No special preparation is usually necessary.

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.

The RF test is used mainly in the diagnosis of rheumatoid arthritis, although the test result can be positive in many other diseases as well as in healthy people.

RF is an antibody that attaches to a substance in the body called immunoglobulin G (IgG), forming a molecule known as an immune complex. This immune complex can activate various inflammatory processes in the body.

About 80% of patients with rheumatoid arthritis have positive RF tests.