Also known as:Antibodies to Saline-extracted Antigens; Anti-RNP; Anti-Ribonucleoprotein; Anti-U(1)RNP; Anti-SmRNP; Anti-SSA; SSA (Ro); Anti-Sjogren Syndrome A; Anti-SSB; SSB (La); Anti-Sjogren Syndrome B; Anti-Sm; Smith Antibody; Scl-70; Anti-Topoisomerase; Scleroderma Antibodies; Anti-Jo-1; Antihistidyl Transfer RNA Synthase Antibodies
Formal name:Extractable Nuclear Antigen Antibodies
Related tests:ANA; Autoantibodies; Anti-dsDNA
Why Get Tested?
To help diagnose and distinguish between autoimmune disorders as well as to monitor autoimmune disease progression
When to Get Tested?
When your antinuclear antibody (ANA) test is positive; when you have symptoms that suggest an autoimmune disorder; when monitoring the activity of an autoimmune disorder
A blood sample drawn from a vein in your arm
Test Preparation Needed?
How is it used?
The ENA panel is usually ordered following a positive ANA test for people who have signs and symptoms of an autoimmune disorder.
The 4-test ENA panel is used to help diagnose mixed connective tissue disease (MCTD), systemic lupus erythematosus (SLE), and Sjogren syndrome. The 6-test ENA panel can also help identify scleroderma and polymyositis/dermatomyositis.
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 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
- Sensitivity to ultraviolet light
- Raynaud phenomenon
- Neurologic symptoms such as seizures, depression, psychoses
- Hemolytic anemia (low red blood cell count) or leukopenia (low white blood cell count)
In most cases, an ENA panel will not be ordered 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 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 health 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 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 Sjogren's syndrome; may also be positive with SLE and scleroderma|
|Anti-SS-B (La)||Positive result seen in 60% of those with Sjogren'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; 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.
What is being tested?
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 ordered separately.
A 4-test ENA panel will include:
|Autoantibody Test||Formally Known As|
|Anti-SS-A (Ro)||Anti-Sjogren Syndrome A|
|Anti-SS-B (La)||Anti-Sjogren 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.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
- 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 doctor's office?
No. The ENA tests require specialized equipment and skilled laboratory personnel. Your sample will need to be sent to a laboratory that performs these tests.
- 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.
- Should everyone have an ENA panel done?
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.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.