Extractable Nuclear Antigen Antibodies (ENA) Panel
A blood sample drawn from a vein in your arm
An extractable nuclear antigen (ENA) panel detects the presence of 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 and represent six main proteins (Ro, La, Sm, RNP, Scl-70 and Jo1).
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. Autoantibody association can aid in the diagnosis of an autoimmune disorder and help distinguish between other autoimmune 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 healthcare practitioners and patients it serves. Individual ENA panel tests can also be ordered 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|
|Anti-Scl-70||Scleroderma Antibodies; anti-topoisomerase|
|Anti-Jo-1||Anti-Histidyl Transfer RNA Synthase Antibodies|
How is the test used?
The ENA panel may be used as follow-up testing to a positive ANA test to help diagnose an autoimmune disorder. Testing may be used to help distinguish between autoimmune disorders as well as to monitor autoimmune disease progression.
The 4-test ENA panel is used to help diagnose mixed connective tissue disease (MCTD), lupus (SLE), and Sjögren syndrome. The 6-test ENA panel can also help identify scleroderma and polymyositis/dermatomyositis. For more on these diseases, see the links under Related Content below.
An ENA panel may also be used to monitor the activity of a particular autoimmune disorder in conjunction with clinical examination.
When is it ordered?
An ENA panel is ordered 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
- Hair loss or loss of scalp hair
- Sensitivity to ultraviolet light
- Raynaud phenomenon
- Protein in the urine (proteinuria)
- Neurologic symptoms such as seizures, depression, psychoses
- Hemolytic anemia (low red blood cell count) or leukopenia (low white blood cell count)
An ENA panel will not be ordered when a person has a negative ANA test. The ANA test evaluates the presence or absence of autoantibodies, while the ENA panel aims to determine to what proteins in the cell nucleus the autoantibodies recognize. If an ANA test is negative, 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 and symptoms 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. A healthcare practitioner also may order 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 aid in detecting and distinguishing 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 the person's clinical findings (signs and symptoms). If someone has clinical findings that suggest a specific autoimmune disorder and the corresponding ENA autoantibody is positive, then it is likely that the person has that condition.
If an individual has symptoms but the autoantibody is not present, it may mean that 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 lupus and scleroderma Anti-Sm Positive result seen in 30% of those with lupus; very specific antibody marker for this disease Anti-SS-A (Ro) Positive result seen in 75% of those with Sjögren syndrome; may also be positive with lupus and scleroderma Anti-SS-B (La) Positive result seen in 60% of those with Sjögren syndrome; may also be positive with lupus and scleroderma; rarely present without anti-SS-A Anti-Scl-70 Positive result seen in 60% of those with scleroderma; 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 clinically relevant and routinely tested.
Will my ENA autoantibodies ever go away?
Levels may fluctuate, but once a person has developed an autoantibody, he or she will continue to have it.
Can the ENA panel be performed at my healthcare practitioner's office?
How long will it take for results?
This depends on the laboratory performing the testing. Since this is specialized testing and your sample may be sent to a reference laboratory, it may take several days for results to be available.
My doctor ordered 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 ordered and your doctor is interested in additional tests, he or she can order the others separately as needed to ensure that nothing is missed.