Anti-smooth muscle antibody

How the Test is Performed:
Adult or child:
Blood is drawn from a vein ( venipuncture ), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (fill with blood). A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding .

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to Prepare:
Adults:
No special preparation is necessary.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:



How it Feels:
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 .

Risks:

  • excessive bleeding
  • fainting or feeling lightheaded
  • hematoma (blood accumulating under the skin)
  • infection (a slight risk any time the skin is broken)
  • multiple punctures to locate veins



Why this Test is Performed:
This test is performed when a disorder that can trigger the body to form antibodies against smooth muscle is suspected. These disorders include hepatitis and cirrhosis .

Normal Values:
No presence of antibodies is normal.

Abnormal Results:
Up to 90% of people with chronic active hepatitis , and 25 to 40% of those with biliary cirrhosis and idiopathic cirrhosis, are positive for this test (compared to less than 5% of normal people). Anti-smooth muscle antibodies are also commonly present in infectious mononucleosis and some malignant (growing worse and resisting treatment) tumors. Anti-smooth muscle antibody tests also help distinguish lupoid hepatitis from systemic lupus erythematosus .

Cost:
The estimated cost is $48, and it is part of an ANA panel .

Special Considerations:
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.