Anti-smooth muscle antibody
DefinitionAnti-smooth muscle antibody is a blood test that detects the presence of antibodies against smooth muscle.
How the test is performedBlood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How to prepare for the testNo special preparation is needed.
How the test will feelWhen 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 performedYour 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 ValuesNormally, 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 meanA positive test may be due to:Chronic active hepatitisCirrhosisInfectious mononucleosisThe test also helps distinguish autoimmune hepatitis from systemic lupus erythematosus.
What the risks areVeins 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 bleedingFainting or feeling light-headedHematoma (blood accumulating under the skin)Infection (a slight risk any time the skin is broken)