Rheumatoid Factor: About This Test

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What is it?

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

A high RF level can be caused by several autoimmune diseases, including rheumatoid arthritis, and some infections. Sometimes an elevated level of RF is present in healthy people.

Why is this test done?

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

How can you prepare for the test?

  • In general, you don't need to prepare before having this test. Your doctor may give you some specific instructions.

What happens during the test?

  • A health professional takes a sample of your blood.

What else should you know about the test?

  • A doctor always uses the results of an RF test along with information gained from a medical history and a physical examination before diagnosing rheumatoid arthritis.
  • Your results will include an explanation of what a "normal" result is. This is called a "reference range." It is just a guide. Your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed 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.

How long does the test take?

  • The test will take a few minutes.

What happens after the test?

  • You will probably be able to go home right away.
  • You can go back to your usual activities right away.

Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor or nurse call line if you are having problems. It's also a good idea to keep a list of the medicines you take. Ask your doctor when you can expect to have your test results.

Where can you learn more?

Go to https://www.healthwise.net/patientEd

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