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. Anti-smooth muscle antibodies are found in autoimmune liver diseases such as primary biliary cholangitis and autoimmune hepatitis (AIH).

Autoimmune hepatitis

If you have chronic liver disease, it’s likely your doctor will perform an ASMA test. The test can help identify whether you may have active AIH.

Viruses are the most frequent cause of hepatitis worldwide. 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 signs and symptoms include:

  • enlarged liver, called hepatomegaly
  • abdominal distension, or swelling
  • tenderness over the liver
  • dark urine
  • pale-colored stools

Additional symptoms include:

  • yellowing of the skin and eyes, or jaundice
  • itching
  • fatigue
  • loss of appetite
  • nausea
  • vomiting
  • joint pain
  • abdominal discomfort
  • skin rash

How is the anti-smooth muscle antibody test 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 antiseptic 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.

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 needle 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

What do the test results mean?

Normal results

Normal results mean that no significant ASMAs are detected in your blood. The result may be reported as a ratio or in units (U). A negative titer, or normal range, is considered to be a ratio less than 1:20 or less than 20 U.

Abnormal results

Detected levels of ASMAs are reported as a ratio or in units (U).

Weakly positive ASMA results are from 1:20 to 1:30, or 20 to 30 U.

Positive AMSA results are greater than 1:30, or greater than 30 U.

Along with autoimmune liver disease, a test that comes back positive for ASMAs may also be due to:

An F-actin antibody test, in addition to an ASMA test, may improve the ability to detect autoimmune hepatitis over other conditions. Because test results require interpretation, especially in relation to other tests that may have been performed, it’s important to talk to your doctor about your specific results.

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 70 percent of those who develop it.

Autoimmune hepatitis can eventually result in:

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

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