Anti-smooth muscle antibody
Definition
Anti-smooth muscle antibody is a blood test that detects the presence of antibodies against smooth muscle.
How the Test is Performed
A blood sample is needed. This may be taken through a vein. The procedure is called a venipuncture.
How to Prepare for the Test
No special preparation is needed.
How the Test Will Feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the Test is Performed
Your doctor may order this test if you have signs of certain diseases (such as hepatitis and cirrhosis) that can trigger the body to form antibodies against smooth muscle.
Normal Results
Normally, there are no antibodies present.
Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
A positive test may be due to:
- Chronic active hepatitis
- Cirrhosis
- Infectious mononucleosis
The test also helps distinguish autoimmune hepatitis from systemic lupus erythematosus.
Risks
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)