At a glance
Also known as
SMA; ASMA; F-actin antibody; anti-smooth muscle antibody
Why get tested?
To help diagnose autoimmune hepatitis and distinguish it from other causes of liver injury
When to get tested?
When a patient has hepatitis that the doctor suspects may be due to an autoimmune-related process
A blood sample drawn from a vein in your arm
Test preparation needed?
What is being tested?
This test measures the amount of smooth muscle antibodies (SMA) in the blood. SMAs are produced by the body’s to work against its own . The production of SMA is strongly associated with chronic autoimmune hepatitis but may also be seen in other forms of liver disease and with other autoimmune disorders such as primary biliary cirrhosis. Autoimmune hepatitis presents as an acute or chronic of the liver that is not caused by another discernable cause (such as a viral infection, drug, toxin, hereditary disorder or alcohol abuse). It can lead to (liver damage and scarring) and, in some cases, to liver failure.
There are 3 subtypes of SMA antibodies, which reflect their staining pattern when measured by indirect : SMA-V, SMA-VG and SMA-VGT, the latter often called just SMA-T.
In adults, the SMA-T pattern is strongly correlated with auto-immune hepatitis, though when treated any pattern may be present (the antibodies may even disappear).
In children, the antibodies may be present at lower level () than adults and the SMA-V pattern may also indicate autoimmune hepatitis. In adults, SMA-V or VG often indicates a viral infection (hepatitis C), or other auto-immune condition e.g. SLE.
Autoimmune hepatitis can be found in anyone at any age, but about 80% of those affected are women. More than 80% of patients with this disorder will have SMA, either alone or along with antinuclear antibodies (ANA).
Anti-F-actin is an antibody targeted at actin, a specific cytoskeletal protein. Some recent studies suggest that it is a more specific test than SMA for diagnosing autoimmune liver disease, with about 52% to 85% of those affected having the anti-F-actin antibody. Anti-F-actin antibody measurements are only available in a few laboratories and these assays lack sensitivity at present.
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.
Will SMA ever go away?
If it is due to a temporary condition, such as infectious mononucleosis, SMA may drop below detectible levels once the condition has resolved. If SMA is produced because of autoimmune hepatitis, then it will be present throughout the patient’s life, although levels may vary over time. The SMA level is not a reliable indicator of liver disease. Treatment for the liver disease will affect the level of SMA.
Can I have more than one cause of hepatitis?
Yes. For instance, autoimmune hepatitis can co-exist with a viral hepatitis (such as hepatitis C) and can be exacerbated by liver damage caused by alcohol abuse. Since the treatment of hepatitis depends on the cause, it is very important that your doctor understands the underlying cause(s) of your condition.
How fast does autoimmune hepatitis progress?
The course and severity of autoimmune hepatitis is hard to predict. It may be acute or chronic. Many patients will have no or few symptoms for many years and are diagnosed when routine liver tests are abnormal. Occasionally, people present with severe acute liver failure from autoimmune hepatitis.