The rheumatoid factor is an auto-antibody that can be produced in some autoimmune diseases and that reacts against IgG, forming immune complexes that attack and destroy healthy tissues, such as joint cartilage, for example.
Thus, the identification of rheumatoid factor in the blood is important to investigate the presence of autoimmune diseases, such as lupus, rheumatoid arthritis or Sjögren's syndrome, which normally present high values of this protein.
How the exam is done
The measurement of rheumatoid factor is made from a small blood sample that must be collected in the laboratory after fasting for at least 4 hours.
The collected blood is sent to the laboratory, where the test will be carried out to identify the presence of the rheumatoid factor. Depending on the laboratory, the identification of the rheumatoid factor is done by means of the latex test or the Waaler-Rose test, in which the specific reagent for each test is added to a drop of blood from the patient, then homogenized and after 3 5 minutes, check for agglutination. If the presence of lumps is verified, the test is said to be positive, and it is necessary to perform further dilutions to verify the amount of rheumatoid factor present and, thus, the degree of the disease.
As these tests can take more time, the automatic test, known as nephelometry, is more practical in laboratory practices, as it allows several tests to be carried out at the same time and dilutions are made automatically, being only informed to the laboratory professional and the doctor the exam result.
The result is given in titles, with a title of up to 1:20 being considered normal. However, results greater than 1:20 do not necessarily indicate rheumatoid arthritis, and the doctor should order other tests.
What may be the altered rheumatoid factor
The examination of rheumatoid factor is positive when its values are above 1:80, which suggests rheumatoid arthritis, or between 1:20 and 1:80, which can mean the presence of other diseases, such as:
- Lupus erythematosus; Sjogren's syndrome; Vasculitis; Scleroderma; Tuberculosis; Mononucleosis; Syphilis; Malaria; Liver problems; Heart infection; Leukemia.
However, as the rheumatoid factor may also be altered in healthy people, the doctor may order other tests to confirm the presence of any of the diseases that increase the factor. Because the result of this test is quite complex to interpret, its result must always be evaluated by a rheumatologist. Learn all about Rheumatoid Arthritis.
