المساهمات : 4
تاريخ التسجيل : 24/08/2008
|موضوع: Antinuclear Antibody test الخميس سبتمبر 11, 2008 10:43 pm|| |
ANAAlso known as: Antinuclear Antibody test, Fluorescent Antinuclear Antibody, FANA, Extractable Nuclear Antigen Antibodies, ENA
Formal name: Antinuclear Antibody Test
Related tests: Autoantibody tests The Test How is it used?The ANA test is ordered to help screen for autoimmune disorders and is most often used as one of the tests to diagnose systemic lupus erythematosus (SLE). Depending on the patient’s symptoms and the suspected diagnosis, ANA may be ordered along with one or more other autoantibody tests. Other laboratory tests associated with presence of inflammation, such as erythrocyte sedimentation rate (ESR) and/or C-reactive protein (CRP) may also be ordered. ANA may be followed by additional tests that are considered subsets of the general ANA test and that are used in conjunction with the patient’s clinical history to help rule out a diagnosis of other autoimmune disorders. When is it ordered?The ANA test is ordered when a patient shows signs and symptoms that are associated with SLE or another autoimmune disorder. It may also be ordered when a patient has been diagnosed with an autoimmune disorder and the doctor suspects that the patient may have developed an additional autoimmune disorder. Patients with autoimmune disorders can have a wide variety of symptoms such as low-grade fever, joint pain, fatigue, and/or unexplained rashes that may change over time. What does the test result mean?ANA tests are performed using different assays (indirect immunofluorescence microscopy or by enzyme-linked immunoabsorbant assay - ELISA) and results are reported as a titer with a particular type of immunofluroscence pattern (when positive). Low-level titers are considered negative, while increased titers, such as 1:320, are positive and indicate an elevated concentration of antinuclear antibodies. ANA shows up on indirect immunofluorescence as fluorescent patterns in cells that are fixed to a slide that is evaluated under a microscope. Different patterns are associated with a variety of autoimmune disorders. Some of the more common patterns include:
An example of a positive result might be: “Positive at 1:320 dilution with a homogenous pattern.” A positive ANA test result may suggest an autoimmune disease, but further specific testing is required to assist in making a final diagnosis. ANA test results can be positive in people without any known autoimmune disease. While this is not common, the frequency of a false positive ANA result increases as people get older. Also, ANA may become positive before signs and symptoms of an autoimmune disease develop, so it may take time to tell the meaning of a positive ANA in a person who does not have symptoms. Most positive ANA results don't have significance, so physicians should reassure their patients but should also still be vigilant for development of signs and symptoms that might suggest an autoimmune disease. About 95% of SLE patients have a positive ANA test result. If a patient also has symptoms of SLE, such as arthritis, a rash, and autoimmune thrombocytopenia, then he probably has SLE. In cases such as these, a positive ANA result can be useful to support SLE diagnosis. Two subset tests for specific types of autoantibodies, such as anti-dsDNA and anti-SM, may be ordered to help confirm that the condition is SLE. A positive ANA can also mean that the patient has drug-induced lupus. This condition is associated with the development of autoantibodies to histones, which are water soluable proteins rich in the amino acids lysine and arginine. An anti-histone test may be ordered to support the diagnosis of drug-induced lupus. Other conditions in which a positive ANA test result may be seen include:
- Homogenous (diffuse) - associated with SLE and mixed connective tissue disease
- Speckled - associated with SLE, Sjogren’s syndrome, scleroderma, polymyositis, rheumatoid arthritis, and mixed connective tissue disease
- Nucleolar - associated with scleroderma and polymyositis
- Outline pattern (peripheral) -associated with SLE
A doctor must rely on test results, clinical symptoms, and the patient’s history for diagnosis. Because symptoms may come and go, it may take months or years to show a pattern that might suggest SLE or any of the other autoimmune diseases. A negative ANA result makes SLE an unlikely diagnosis. It usually is not necessary to immediately repeat a negative ANA test; however, due to the episodic nature of autoimmune diseases, it may be worthwhile to repeat the ANA test at a future date. Aside from rare cases, further autoantibody (subset) testing is not necessary if a patient has a negative ANA result. Is there anything else I should know?Some drugs and infections as well as other conditions mentioned above can give a false positive result for the ANA test. About 3% - 5% of Caucasians may be positive for ANA and it may reach as high as 10% - 37% in healthy individuals over the age of 65. Some medications may bring on a condition that includes SLE symptoms, called drug-induced lupus. When the drugs are stopped, the symptoms usually go away. Although many medications have been reported to cause drug-induced lupus, those most closely associated with this syndrome include hydralazine, isoniazid, procainamide, and several anticonvulsants.
- Sjögren’s syndrome: Between 40% and 70% of patients with this condition have a positive ANA test result. While this finding supports the diagnosis, a negative result does not rule it out. The doctor may want to test for two subsets of ANA: Anti-SS-A (Ro) and Anti-SS-B (La). The frequency of autoantibodies to SSA in patients with Sjögren’s can be 90% or greater.
- Scleroderma: About 60% to 90% of patients with scleroderma have a positive ANA finding. In patients who may have this condition, ANA subset tests can help distinguished two forms of the disease, limited versus diffuse. The diffuse form is more severe. Limited disease is most closely associated with the anticentromere pattern of ANA staining (and the anticentromere test), while the diffuse form is associated with autoantibodies to the anti–Scl-70.
- A positive result on the ANA also may show up in patients with Raynaud’s disease, rheumatoid arthritis, dermatomyositis, mixed connective tissue disease, and other autoimmune conditions.