RA factors ....are they always true?

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   RA factors....The topic at hand: 

What is seronegative ra factor
The rheumatoid factor is a blood immunology test. Some abnormal antibodies (special proteins produced by B-lymphocytes of the immune system in response to substances such as an infectious agents) are often found in the blood of people with rheumatoid arthritis. 

This test is often (70 percent to 80 percent) positive in people with rheumatoid arthritis. Laboratories usually report results in "International Units." 

A result of over 40 units may be considered abnormal and results can go up to 2,000 units or more, or it may be expressed as a titer (a number to indicate the dilution of blood at which the rheumatoid factor is measured). Tests may be negative during the first several months, making this test less useful in early diagnosis. These factors are also found in healthy people and in patients with other diseases, but less frequently than in rheumatoid arthritis. 

Rheumatoid arthritis is never diagnosed solely based upon a positive RF (rheumatoid factor) test. A positive RF test in conjunction with a physical exam (and other tests as needed) that suggests RA can help make a diagnosis. RF can be positive in people who have no disease at all and is not specific to RA. Other diseases and conditions, including certain infections such as Lyme disease, periodontal disease, and even the flu, can cause a positive or elevated RF. In some cases, a person can have RA and not have a positive RF test. This is referred to as seronegative RA. 

RE seropositivity in patients with RA is associated with a more severe disease course. Extra-articular manifestations are seen almost exclusively in RF-positive patients. 

Seronegative RA is a distinct, though usually less aggressive, form of the disease. Some investigators believe that RE-negative patients are in an early phase along the disease spectrum, as some of them eventually do seroconvert. Patients who become RE positive as their disease progresses have courses parallel to those of initially seropositive patients. 

http://www.arthritis-treatment-and-relief.com/what-is-seronegative-ra-factor.html