Smooth Muscle Antibody (SMA) Test
Reviewed
Also called: anti-smooth muscle antibody, ASMA, actin antibody, ACTA, F-actin antibody
This test looks for smooth muscle antibodies (SMAs) in a sample of your blood. SMAs are autoantibodies that mainly attack the liver.
Specimen: blood
Why this test may be ordered
- You may need an SMA test if you have symptoms of autoimmune hepatitis, such as fatigue, jaundice, abdominal pain, joint pain, nausea, skin conditions, loss of appetite, dark urine, or light-colored stool.
- You may also need this test if you had abnormal results on a routine blood test (e.g., comprehensive metabolic panel) that suggests liver inflammation or damage.
Preparation and collection
You don't need any special preparations for an SMA test.
A health care professional will take a blood sample from a vein in your arm, using a small needle. This usually takes less than five minutes.
There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
Understanding results
Diagnosing autoimmune hepatitis can be difficult. To understand what your SMA test results mean, your provider will consider the results of other tests you've had.
- Positive: High levels of SMAs often mean you have type 1 autoimmune hepatitis. Limitation: But this test can't diagnose the disease. Next step: If you have high levels of both SMAs and ANAs, your provider may suggest a biopsy to remove a small sample of liver tissue for testing.
- Negative: A negative SMA test result means SMAs were not found in your blood sample. You're unlikely to have type 1 autoimmune hepatitis. Limitation: But if you had a test that showed you have anti-LKM-1 antibodies, you may have type 2 autoimmune hepatitis. Next step: You may need a biopsy to confirm the diagnosis.
- There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.
- This test alone cannot diagnose autoimmune hepatitis; results must be interpreted alongside other tests.
- It is possible for autoimmune hepatitis to be caused by other autoantibodies that are not commonly tested, so a negative result does not completely rule out the condition.
What to do next
Your provider can explain what these results say about your health. If you have questions about your results, talk with your provider.
- What do my SMA test results mean in combination with my other test results?
- Do I need any follow-up tests, such as a liver biopsy?
- What are the next steps if my results suggest autoimmune hepatitis?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: Smooth Muscle Antibody (SMA) Test