What Is an Anti-Smooth Muscle Antibody (ASMA) Test?
An anti-smooth muscle antibody (ASMA) test detects antibodies
that attack smooth muscle. This test is performed on a blood sample.
Your immune system detects substances that may be harmful in your
body. These substances are called antigens.
Viruses and bacteria are examples of antigens. When your immune system recognizes
an antigen, it produces a protein known as antibody to attack it.
Every antibody produced is unique, and each one defends against
only one type of antigen. Sometimes antibodies are mistakenly produced against
the body’s own healthy cells. These are called autoantibodies. If the body starts attacking itself, it causes
an autoimmune disorder.
An ASMA test looks for the one type of autoantibody that attacks
smooth muscle. Autoimmune diseases that attack smooth muscle include the liver
diseases cirrhosis and hepatitis.
An ASMA test is often performed in patients who have chronic
liver disease. It can confirm a diagnosis of chronic active autoimmune
Viruses are the most frequent causative agents of hepatitis.
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
AIH symptoms include:
- enlarged liver, or hepatomegaly
- abnormal blood vessels visible on the skin,
which are called spider angiomas
- abdominal distension, or swelling
- dark urine
- pale-colored stools
Additional symptoms that may occur include:
- yellowing of the skin and eyes, or jaundice
- itching caused by a buildup of toxins and bile
- loss of appetite
- 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 patients with autoimmune hepatitis. They are not found in patients
How the Anti-Smooth Muscle Antibody Test Is Performed
The ASMA test is performed on a blood sample. It can be done at a
hospital, clinic, or laboratory.
To perform the test, a healthcare professional will take a blood
sample. The blood sample is usually taken in the following way:
- First, an elastic band is wrapped around your
upper arm. This stops blood flow and makes your veins more visible. This makes
it easier to insert the needle.
- After a vein is located, the healthcare
professional will clean your skin is cleaned with alcohol and insert a needle.
A tube is attached to collect the blood. When the needle is inserted, you may
feel a brief pinching or stinging sensation. There may also be some minor
discomfort when the needle is positioned in the vein
- After enough blood is collected, they’ll remove
the elastic band from your arm. As the needle is removed, they’ll 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.
You may feel some throbbing at the site after the needle is
removed. Many people don’t feel anything at all. Serious discomfort is rare.
You don’t need to do anything to prepare for an ASMA test.
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 needle is removed can minimize bruising.
Continued bleeding after the needle is removed is a potential
risk for some people. Tell the test administrator if you’re taking blood
thinners or have problems with bleeding or clotting.
Inflammation of the vein may occur in rare cases after the blood
sample is taken. This condition is known as phlebitis. Applying a warm compress several times a day can be
done to treat it.
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 mean that no ASMAs are detected in the blood.
A test that comes back positive for ASMAs may be due to:
- chronic active autoimmune hepatitis
- infectious mononucleosis
A diagnosis of autoimmune hepatitis means that the immune system
is mistakenly producing antibodies that attack healthy cells in the liver. Anyone
can be diagnosed with autoimmune hepatitis, but women make up 80
percent of affected individuals.
This attack can eventually result in:
- destruction of the liver
- 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.