A blood sample taken from a vein in your arm
An extractable nuclear antigen (ENA) panel detects the presence of one or more autoantibodies in the blood that react with proteins in the cell nucleus. These proteins are known as "extractable" because they can be removed from cell nuclei using saline.
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.
Certain autoimmune disorders are characteristically associated with the presence of one or more anti-ENA antibodies. This association can be used to help diagnose an autoimmune disorder and to distinguish between disorders.
The ENA panel typically consists of a group of 4 or 6 autoantibody tests. The number of tests performed will depend on the laboratory and the needs of the health practitioners and patients it serves. Individual ENA panel tests can also be requested separately.
A 4-test ENA panel will include:
|Autoantibody Test||Formally Known As|
|Anti-SS-A (Ro)||Anti-Sjögren Syndrome A|
|Anti-SS-B (La)||Anti-Sjögren Syndrome B|
A 6-test ENA panel will include the four tests listed above as well as:
|Autoantibody Test||Formally Known As|
|Scl-70||Scleroderma Antibodies; anti-topoisomerase|
|Anti-Jo-1||Antihistidyl Transfer RNA Synthase Antibodies|
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
The 4-test ENA panel is used to help diagnose mixed connective tissue disease (MCTD), systemic lupus erythematosus (SLE), and Sjögren syndrome. The 6-test ENA panel can also help identify scleroderma (systemic sclerosis) and polymyositis/dermatomyositis (inflammatory myopathies).
For more on these diseases, visit the National Institute of Arthritis and Musculoskeletal and Skin Diseases web site.
An ENA panel may also be used to monitor the activity of a particular autoimmune disorder.
When is it requested?
An ENA panel is requested when a person has signs and 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:
- Fever and persistent fatigue
- Muscle pain
- Joint swelling and/or pain
- Skin rash
- Sensitivity to ultraviolet light
- Raynaud phenomenon
- Neurologic symptoms such as seizures, depression, psychoses
- Haemolytic anaemia (low red blood cell count) or leukopenia (low white blood cell count)
In most cases, an ENA panel will not be requested when a person has a negative ANA test. If no antinuclear antibodies are present, then the person is extremely unlikely to test positive for a specific antinuclear antibody (which is what the ENA panel tests).
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 requested 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. A health practitioner also may request testing to monitor the activity and/or progression of a known autoimmune disorder.
What does the test 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 to detect and distinguish between different 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 the individual has not yet developed the autoantibody, or it may mean that the person's symptoms are due to another condition.
Interpretation of results for the tests included in an ENA panel are provided in the table below. A positive test result means that the person has more of that autoantibody in their blood than the designated reference value.
Autoantibody Test Results That Support an Autoimmune Disorder Diagnosis Anti-RNP Positive result seen in 95-100% of mixed connective tissue disease (MCTD) cases; may also be positive with SLE and scleroderma Anti-Sm Positive result seen in 30% of those with SLE; very specific antibody marker for this disease Anti-SS-A (Ro) Positive result seen in 75% of those with Sjögren's syndrome; may also be positive with SLE and scleroderma Anti-SS-B (La) Positive result seen in 60% of those with Sjögren's syndrome; may also be positive with SLE and scleroderma; rarely present without anti-SS-A Scl-70 Positive result seen in 60% of those with scleroderma (systemic sclerosis); highly specific antibody marker for this disease Anti-Jo-1 Positive result seen in 30% of those with polymyositis; may be positive with pulmonary fibrosis
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 antigens have been identified in this way, but only a few are routinely tested.
Will my ENA autoantibodies ever go away?
Can the ENA panel be performed in my doctor's surgery?
No. The ENA tests require specialised equipment and skilled laboratory personnel. Your sample will need to be sent to a laboratory that performs these tests.
My doctor requested only a 4-test ENA panel, not a 6-test ENA panel. Will something be missed?
The panel performed will usually be the one offered by the laboratory that tests your sample. If a 4-test panel is requested and your doctor is interested in additional tests, he or she can request the others separately as needed to ensure that nothing is missed.
Should everyone have an ENA panel done?