Smooth Muscle Antibody (SMA) Test

The Smooth Muscle Antibody (SMA) test is a blood test used to detect the presence of antibodies against smooth muscle cells in the body. These antibodies are a type of autoantibody, which means they are produced by the immune system and target the body's own tissues.

What do SMAs target?

SMAs target actin, a protein found in smooth muscle cells, which are a type of non-striated muscle cell. Smooth muscle cells are found in various parts of the body, including the digestive tract, blood vessels, and airways.

What is the purpose of the SMA test?

The SMA test is used to help diagnose autoimmune disorders, such as:

• Autoimmune hepatitis: a condition in which the immune system attacks the liver
• Primary biliary cirrhosis: a condition in which the immune system attacks the bile ducts in the liver
• Chronic active hepatitis: a condition in which the liver is inflamed and damaged over time

How is the SMA test performed?

The SMA test involves taking a blood sample from a vein, usually in the arm. The blood sample is then sent to a laboratory for analysis.

What are the results of the SMA test?

The results of the SMA test are typically reported as:

• Positive: SMAs are present in the blood, which may indicate an autoimmune disorder
• Negative: SMAs are not present in the blood, which suggests that an autoimmune disorder is less likely
• Titer: a measure of the level of SMAs in the blood, with higher titers indicating more severe disease

Interpretation of results

The interpretation of SMA test results should be done by a healthcare professional, taking into account the patient's medical history, physical examination, and other laboratory test results.

Limitations of the SMA test

The SMA test is not specific for any particular disease and can be positive in various autoimmune disorders. Additionally, some people without autoimmune disorders may have a positive SMA test result.