Rheumatoid factor (RF)

  • Definition
    • Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.

  • How the Test is Performed
    • Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand.

      In infants or young children, a sharp tool called a lancet may be used to puncture the skin.

      • The blood collects in a small glass tube called a pipette, or onto a slide or test strip.
      • A bandage is put over the spot to stop any bleeding.
  • How to Prepare for the Test
    • Most of the time, you do not need to take special steps before this test.

  • How the Test will Feel
    • You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.

  • Why the Test is Performed
  • Normal Results
    • Results are usually reported in 1 of 2 ways:

      • Less than 40 to 60 u/mL
      • Less than 1:80 (1 to 80) titer

      A low number (normal result) most often means you do not have rheumatoid arthritis or Sjögren syndrome. However, some people who do have these conditions still have a "normal" or low RF.

      Normal value ranges may vary slightly among different laboratories. Talk to your health care provider about the meaning of your specific test results.

  • What Abnormal Results Mean
    • An abnormal result means the test is positive, which means a higher level of rheumatoid factor has been detected in your blood.

      • Most people with rheumatoid arthritis or Sjögren syndrome have positive RF tests.
      • The higher the level, the more likely one of these conditions is present. There are also other tests for these disorders that help make the diagnosis.
      • Not everyone with a higher level of RF has rheumatoid arthritis or Sjögren syndrome.

      Your provider may do another blood test (anti-CCP antibody), to help diagnose rheumatoid arthritis.

      People with the following diseases may also have higher levels of RF:

      Higher-than-normal levels of RF may be seen in people with other medical problems. However, these higher RF levels cannot be used to diagnose these other conditions:

      In some cases, people who are healthy and have no other medical problem will have a higher-than-normal RF level.

  • References
    • Andrade F, Darrah E, Rosen A. Autoantibiodies in rheumatoid arthritis. In: Firestein GS, Budd RC, Gabriel SE, McInnes IB, O'Dell JR, eds. Kelley's Textbook of Rheumatology. 9th ed. Philadelphia, PA: Elsevier Saunders; 2012:chap 56.

      Mason JC. Rheumatic diseases and the cardiovascular system. In: Holcomb GW, Murphy JD, Ostlie DJ, eds. Ashcraft's Pediatric Surgery. 6th ed. Philadelphia, PA: Elsevier Saunders; 2014:chap 84.