What is being tested?
An ENA (Extractable Nuclear Antigen Antibodies) panel detects the presence of one or more specific autoantibodies in the blood. Autoantibodies are produced when a person's immune system mistakenly targets and attacks the body's own tissues. This attack can cause inflammation, tissue damage, and other signs and symptoms that are associated with an autoimmune disorder.
ENA are a subset of antinuclear antibodies (ANA), antibodies directed against proteins found in the nucleus of cells. Certain autoimmune disorders are characteristically associated with the presence of one or more extractable nuclear antigen antibodies. This association can be used to help diagnose an autoimmune disorder and to distinguish between disorders.
The ENA panel is typically a group of 6-10 autoantibody tests. The number of tests offered will depend on the laboratory and the needs of the doctors and patients it serves. ENA panel tests, and other less common ENA tests, may be able to be ordered separately depending on the laboratory.
The most common panel in Australia at present would include at least these antibodies:
|AUTOANTIBODY||ALSO KNOWN AS|
|Anti-RNP||Anti-U(1) RN, Anti- Ribonucleoprotein|
|Anti-SSA (Ro)||Anti-Sjögren Sydnrome A|
|Anti-SSB (La)||Anti-Sjögren Syndrome B|
|SCI-70||Scleroderma Antibodies; anti-topoisomerase|
|Anti-Jo-1||Antihistidyl Transfer RNA Synthase Antibodies|
How is it used?
The ENA panel is usually ordered following a positive ANA test in people who have clinical signs of an autoimmune disorder. ENA panel is used to help diagnose mixed connective tissue disease (MCTD), systemic lupus erythematosus (SLE), Sjögren syndrome, scleroderma and myositis.
For more on these diseases, visit the Australian Society of Clinical Immunology and Allergy and the Australian Rheumatology Association web site.
An ENA panel may also be ordered if a doctor suspects that a person with a known autoimmune disorder has developed an additional disorder.
When is it requested?
An ENA panel is ordered when a person has symptoms that could be due to an autoimmune disorder and has a positive ANA test. Signs and symptoms of autoimmune disorders are highly variable and can involve several different areas of the body. They may include:
The ENA panel, or one or more of its component tests, may be repeated when initial test results are negative but clinical signs persist. Testing may also be ordered when a person has been diagnosed with an autoimmune disorder and at some point develops symptoms that may be due to an additional autoimmune disorder.
What does the result mean?
Diagnoses of autoimmune diseases are typically based on the characteristic signs and symptoms and on results of autoantibody tests. ENA panel results help support the diagnosis of autoimmune disorders. Studies have shown that each of these autoantibodies is frequently detected in people who have a specific autoimmune disorder and is less frequently detected or not detected in those without the disease.
The pattern of positive and negative results obtained with an ENA panel is evaluated in conjunction with a person's clinical findings. If someone has symptoms that suggest a specific autoimmune disorder and the corresponding ENA autoantibody is positive, then it is likely that the person has that condition.
If a person has symptoms but the autoantibody is not present, it could mean that they have not yet developed the autoantibody, or it may mean that the person's symptoms are due to another condition.
The interpretation of ENA panel testing is provided in the table below:
|AUTOANTIBODY||FINDINGS THAT HELP SUPPORT THE DIAGNOSIS OF AN AUTOIMMUNE DISORDER|
|Anti-RNP||Positive in 95- 100% of MCTD; may also be positive with SLE, scleroderma and rheumatoid arthritis.|
|Anti-Sm||Positive in 5-10% of those with SLE; very specific for this disease|
|Anti-SSA (Ro)||Positive in up to 100% of those with Sjögren's syndrome; may also be positive with SLE|
|Anti-SSB (La)||Positive in up to 100% of those with Sjögren's syndrome; may also be positive with SLE and scleroderma; rarely present without anti-SSA|
|SCI-70||Positive in up to 20% of those with Scleroderma|
|Anti-Jo-1||Positive in up to 20% of idiopathic inflammatory myositis including those with skin and lung involvement|
Is there anything else I should know?
ENA are referred to as "extractable" or "saline-extracted" because of the laboratory method originally used to discover and work with these antigens. More than 100 ENA antigens have been identified, but only a few are routinely tested.
Levels may fluctuate and loss of the ability to detect some ENA antibodies may occur in disease remission.
No. The ENA tests require specialised equipment and skilled laboratory scientists. Your sample will need to be sent to a laboratory that performs these tests.
Autoantibody testing is only necessary when a person has symptoms that suggest an autoimmune disorder. Most people will never need to have an ENA panel performed.
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