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 hepatitis.
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 failure.
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 with lupus.
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.
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
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.