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Anti-Smooth Muscle Antibody

What is an anti-smooth muscle antibody (ASMA) test?

An anti-smooth muscle antibody (ASMA) test detects antibodies that attack smooth muscle. This test requires a blood sample.

Your immune system detects substances called antigens that may be harmful to your body. Viruses and bacteria are covered with antigens. When your immune system recognizes an antigen, it makes a protein called an antibody to attack it.

Every antibody is unique, and each one defends against only one type of antigen. Sometimes your body mistakenly makes autoantibodies, which are antibodies that attack your body’s own healthy cells. If your body starts attacking itself, you may develop an autoimmune disorder.

An ASMA test looks for the one type of autoantibody that attacks smooth muscle. Autoimmune diseases caused by attacking smooth muscle include two liver diseases, cirrhosis and hepatitis.

Autoimmune hepatitis

If you have chronic liver disease, it’s likely your doctor will perform an ASMA test. The test can confirm whether you have chronic active autoimmune hepatitis.

Viruses are the most frequent cause of hepatitis worldwide. Autoimmune hepatitis (AIH) is one exception. This type of liver disease occurs when your immune system attacks your liver cells. AIH is a chronic condition and can result in cirrhosis, or scarring, of the liver and ultimately liver failure.

AIH symptoms include:

  • enlarged liver, called hepatomegaly
  • abnormal blood vessels visible on the skin, called spider angiomas
  • abdominal distension, or swelling
  • dark urine
  • pale-colored stools

Additional symptoms include:

  • yellowing of the skin and eyes, or jaundice
  • itching caused by a buildup of toxins
  • fatigue
  • loss of appetite
  • nausea
  • vomiting
  • joint pain
  • abdominal discomfort

The ASMA test can also distinguish between autoimmune hepatitis and other causes of liver damage, such as systemic lupus erythematosus. ASMAs are present in people with autoimmune hepatitis. ASMAs are not found in people with lupus.

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Procedure

How the anti-smooth muscle antibody test is performed

You don’t need to do anything to prepare for an ASMA test. You can have the test at a hospital, clinic, or laboratory.

To perform the ASMA test, a healthcare professional will get a blood sample from you. Usually, you give a blood sample in the following way:

  1. The healthcare professional wraps an elastic band around your upper arm. This stops blood flow, makes your veins more visible, and makes it easier to insert the needle.
  2. After they find your vein, the healthcare professional cleans your skin with alcohol and inserts a needle with a tube attached to collect the blood. As the needle goes in, you may feel a brief pinching or stinging sensation. You may also have some minor discomfort when the healthcare professional positions the needle in your vein.
  3. After the professional collects enough of your blood, they’ll remove the elastic band from your arm. They remove the needle, and place gauze or a piece of cotton onto the site of the injection and apply pressure. They’ll secure the gauze or cotton with a bandage.

After the needle’s removed, you may feel some throbbing at the site. Many people don’t feel anything at all. Serious discomfort is rare.

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Risk factors

What are the risks?

The ASMA test carries minimal risk. There may be a small amount of bruising at the needle site. Applying pressure on the puncture site for several minutes after the healthcare professional removes the can minimize bruising.

Some people have a potential risk of continued bleeding after the professional’s removed the needle. Tell the test administrator if you’re taking blood thinners or have problems with bleeding or clotting.

In rare cases after you’ve given a blood sample, inflammation of the vein may occur. This condition is known as phlebitis. To treat it, apply a warm compress several times a day.

In very rare cases, having blood drawn may result in:

  • excessive bleeding
  • lightheadedness or fainting
  • a hematoma, which is an accumulation of blood under the skin
  • an infection at the needle site
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Results

What do the test results mean?

Normal results

Normal results mean that no ASMAs are detected in your blood.

Abnormal results

A test that comes back positive for ASMAs may be due to:

A diagnosis of autoimmune hepatitis means that your immune system is mistakenly making antibodies that attack healthy cells in your liver. Anyone can have autoimmune hepatitis, but women make up 80 percent of those who develop it.

Autoimmune hepatitis can eventually result in:

  • destruction of the liver
  • cirrhosis
  • liver cancer
  • the need for a liver transplant

You should discuss your test results with your doctor. They’ll be able to determine the best treatment options for you if any are necessary. 

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