Rheumatoid Factor Test
Rheumatoid factor test is used to measure the amount of rheumatoid factor in the blood. Rheumatoid factors are proteins produced by the body's immune system that can attack healthy tissue in the body. Antibodies are normal protein found in the blood, functioning within the immune system. Rheumatoid factor is an immunoglobulin i.e. antibody that can bind other antibodies. It may be present in 1-2% of the healthy population. In older people aged 65 and above, 20% have elevated level of rheumatoid factor.
Elevated levels of rheumatoid factor in the blood show up as autoimmune diseases, such as rheumatoid arthritis and Sjogren's syndrome. Many a time, rheumatoid factor may be detected in few healthy people and at times some people with autoimmune diseases have normal levels of rheumatoid factor. Patients with negative rheumatoid factor but suffering from the condition are classified as having seronegative rheumatoid arthritis. But largely, healthy people do not produce rheumatoid factor.
A sample of blood is drawn from the vein in the arm and sent to the laboratory for test. The RF test helps to diagnose rheumatoid arthritis and may also help the physician choose the line of treatment. A positive result, i.e. test result indicating the presence of rheumatoid factor in the blood may confirm rheumatoid arthritis in a person. About 80% of adults who have rheumatoid arthritis test high for rheumatoid factor.
This test helps differentiate between rheumatoid and inflammatory arthritis from other types of arthritis. High level of rheumatoid factor may also result from the presence of other autoimmune diseases in the body such as:
When is the test ordered?
Rheumatoid factor test is ordered for persons suffering from the following symptoms:
Rheumatoid arthritis test principle
Rheumatoid factor can be identified in the laboratory by its ability to bind and form clumps with latex particles or red blood cells that have human immunoglobulin (IgG). If the patient being tested has rheumatoid factor, then it attaches to the IgG coating the latex particles causing lumps. This process is called agglutination. Agglutination is a positive reaction that indicates the presence of rheumatoid factor at a detectable level.
Rheumatoid Factor Results
The antibody titer is a test that measures the quantity of the blood that can be diluted before RF antibodies become indistinguishable. The following results will be considered as normal:
Less than 40 - 60 units/ml
Less than 1:80 (1 to 80) titer.
A low number (normal result) generally indicates that the person being tested does not have rheumatoid arthritis or Sjogren syndrome. However, a few people who have the condition may still have a normal or low rheumatoid factor (RF). Normal ranges may vary from laboratory to laboratory.
An abnormal result may mean the test is positive. Most patients with this result may have rheumatoid arthritis or Sjogren's syndrome. The higher the level, the more likely the condition is present. There are other tests that may be used to diagnose the condition.
Optic neuritis is a condition where the optic nerve gets inflamed. Due to the inflammation, light and visual images are not clearly transmitted to the brain. Optic neuritis can be caused by autoimmune diseases such as multiple sclerosis or viral infections such as chicken pox or measles. Optic neuritis is usually the first sign of multiple sclerosis. This condition tends to affect more women than men.
Patients suffering from optic neuritis notice reduced vision. This is more so when the body temperature is elevated. The eyes are sore and painful when moved. There is reduced color perception and diminished peripheral vision. Persons suffering from optic neuritis may have headache and fever. The vision diminishes for about a week and then gradual improvement is noticed. Typically most patients suffering from optic neuritis tend to recover most of their vision within about 6 months.
The ophthalmologist will test the patient's color vision and visual field. Eye pressure and pupillary function will be examined. The optic disc is viewed with indirect ophthalmoscopy. Brain MRI may be taken for testing for multiple sclerosis. Intravenous steroid medication has shown results on those suffering from initial occurrence of optic neuritis.
ANA blood test
Antinuclear antibodies (ANA) refer to the unusual antibodies that are detectable in the blood. ANA are gamma-globulins type of antibodies that are found in patients with certain autoimmune diseases. ANA are directed against certain components found in the nucleus of a cell in the body. These antibodies have the capacity of binding certain structures within the nucleus of the cells. The ANA test was first designed by Dr.George Friou in 1957. The laboratory blood test exposes the antibodies in the serum of the blood to cells. It is then determined whether or not antibodies are present that react to various parts of the nucleus of cells. Hence the term 'anti-nuclear' antibody is used.
Fluorescence techniques are adopted to detect the ANA antibodies in the cells. Thus ANA testing is sometimes referred to as fluorescent antinuclear antibody test (FANA). Nowadays, a method to detect antinuclear antibodies called enzyme linked immunosorbent assay (ELISA) is replacing the previous method of immunofluorescent assay technique. The ELISA method is less likely to produce false positive ANA result than the previous method.
Patterns also give doctors a clue as to the type of illness to look for while evaluating a patient. For instance, the disease Scleroderma shows in nucleolar pattern. If a person does not have any autoimmune disease, it is defined in speckled pattern. An ANA blood test is used in patients who might be suffering from Sjogren's syndrome, rheumatoid arthritis, polymyositis, scleroderma, Hashimoto's thyroiditis, juvenile diabetes mellitus, Addison's disease, vitiligo, pernicious anemia, glomerulonephritis and pulmonary fibrosis. ANA can also be found in patients with conditions that are not considered autoimmune diseases such as chronic infections and cancer.
The result of the ANA test is expressed in titers. A titer of 1 to 80 (1:80) means that antibodies could be last detected when 1 part of the blood sample was diluted by 80 parts of another liquid. Usually this other liquid is a diluted salt solution. A larger second number indicates that the antibodies are present in greater concentration. Therefore a titer of 1 to 320 indicated higher concentration of antibodies in the blood than a titer of 1 to 80. The normal values of ANA blood test is : Titer below 1: 20 or 1:40 depending on the test method used.
Positive ANA test result is suggestive of autoimmune disease. It can also mean that the patient has drug induced lupus. Some drugs and infections can also induce false positive ANA test results. Steroids can cause a false-negative result. Medications, especially antibiotics such as isoniazid, penicillin, and tetracycline, birth control pills, lithium and some diuretics such as chlorthalidone can interfere with the test and affect the accuracy of the ANA test result.
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Bibliography / Reference
Collection of Pages - Last revised Date: September 22, 2019