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. High levels of SMAs are usually a sign of a chronic liver condition called autoimmune hepatitis. The test is mainly used with other tests to help determine if autoimmune hepatitis could be the cause of liver damage.
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. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. 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. Your provider will consider the results of other tests you've had to understand what your SMA test results mean. In general:
- Positive: High levels of SMAs often mean you have type 1 autoimmune hepatitis, but other conditions (e.g., primary biliary cholangitis, infectious mononucleosis, hepatitis C, certain cancers) may also cause moderately high levels. Limitation: This test cannot diagnose the disease on its own. Next step: Prompt
- Negative: SMAs were not found in your blood sample. You are unlikely to have type 1 autoimmune hepatitis. If you have anti-LKM-1 antibodies, you may have type 2 autoimmune hepatitis. Limitation: A negative result does not completely rule out autoimmune hepatitis. Next step: Routine
- 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 will review your SMA results along with other test results and may suggest a liver biopsy to confirm the diagnosis. Talk with your provider about what your results mean for your health.
- 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
U.S. National Library of Medicine: Smooth Muscle Antibody (SMA) Test