Rheumatoid factor (rf) test

A rheumatoid factor (RF) blood test measures the amount of the RF antibody in your blood. The RF antibody can damage normal body tissue.

A high RF level can be caused by diseases like rheumatoid arthritis. It's also caused by some other conditions. Sometimes healthy people have a high level of RF.

A test for rheumatoid factor is done to help support a diagnosis of rheumatoid arthritis.

This test is also done to find out whether a child who has polyarticular juvenile idiopathic arthritis has elevated rheumatoid factor. This can help determine the likely progression of the disease, and the best treatment for it.

A health professional uses a needle to take a blood sample, usually from the arm.

You don't need to do anything before your child has this test.

• A doctor always uses the results of an RF test along with information gained from a medical history, a physical exam, and other tests before diagnosing rheumatoid arthritis.
• Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
• A small number of people have a high RF level but don't have rheumatoid arthritis. A small number of these people will later have rheumatoid arthritis.
• Older adults who don't have rheumatoid arthritis sometimes have a slightly high RF level.