Smooth Muscle Antibody (SMA) Test

This test looks for smooth muscle antibodies (SMAs) in a sample of your blood. High levels of SMAs are usually a sign of a chronic (long-lasting) liver condition called autoimmune hepatitis. Autoimmune hepatitis is a type of autoimmune disease.

Normally, your immune system makes antibodies to attack foreign substances that could make you sick, such as viruses and bacteria. But in autoimmune diseases, your immune system makes certain types of antibodies - called autoantibodies - that attack your body's own healthy cells and organs by mistake. SMAs are autoantibodies that mainly attack the liver.

They are sometimes called anti-smooth muscle antibodies (ASMAs). They get their name because they attack certain proteins that are found in smooth muscle (the muscle that lines the inside of hollow organs, such as your intestines, stomach, and blood vessels). But these proteins are also found in large amounts in liver cells.

When SMAs attack your liver, they cause liver swelling and damage. Without treatment, autoimmune hepatitis can lead to serious liver problems, including cirrhosis and liver failure. Treatment often includes medicines that decrease the activity of your immune system.

Early diagnosis and treatment can lower the chances of developing cirrhosis and other liver conditions linked to autoimmune hepatitis.

Why this test is done

You may need an SMA test if you have symptoms of autoimmune hepatitis. The test is usually ordered after the results of liver function tests show that your liver may be damaged.

Symptoms of autoimmune hepatitis may include:

• Fatigue
• Jaundice (a condition that causes your skin and eyes to turn yellow)
• Abdominal pain in the upper part of your belly
• Joint pain
• Nausea
• Skin conditions, including rashes, psoriasis, acne, or vitiligo (white patches on your skin)
• Loss of appetite
• Dark-colored urine (pee)
• Light colored stool (poop)

In the early stages, autoimmune hepatitis may not cause symptoms. But you may need an SMA test if you had abnormal results on a routine blood test, such as a comprehensive metabolic panel (CMP). A CMP measures several substances made by your liver.

Abnormal amounts of these substances are usually a sign of liver inflammation and/or damage.

How to prepare

You don't need any special preparations for an SMA test.

Sample type

Blood

Other names for this test

anti-smooth muscle antibody, ASMA, actin antibody, ACTA, F-actin antibody