Certain health conditions, including liver disease and hepatitis, cause the immune system to produce anti-smooth muscle antibodies. Doctors use a blood test to check for these antibodies.
Anti-smooth muscle antibodies (ASMAs) attack several structural proteins in smooth muscle, affecting the liver and other tissues.
The presence of ASMA in the blood indicates that a person may have autoimmune hepatitis or another disease that damages the liver.
In this article, we take a close look at the ASMA test, including its uses, the procedure, and how to interpret the results.
Doctors use the test to check for ASMA in the blood. The antibodies attack the smooth muscle in a person's body.
An ASMA test is carried out in the same way as any routine blood test.
Check with a doctor about necessary preparations, such as fasting, though the ASMA test does not usually require any.
During the test, a technician draws blood from a vein in the arm, taking the following steps:
- The person will sit with an arm resting on a table.
- The technician will tie an elastic band around the middle of the upper arm, making the veins more visible.
- The technician will find a suitable vein and rub an antiseptic on the area to clean it.
- They will insert a needle into the vein and draw the necessary amount of blood.
- The technician will remove the needle and apply pressure to the insertion site.
- They will remove the arm band and place an adhesive bandage over the site.
A person will likely feel a slight pinch when the technician inserts the needle. Any discomfort will usually fade after a few seconds.
The technician will send the vial of blood to a laboratory. After testing the blood for the presence of ASMA, the lab will usually return the results to the doctor's office within a few days, though the timing depends on the lab.
Doctors consider the ASMA test a low-risk procedure. Any side effects will be mild and may include bruising around the insertion site or light-headedness.
Anyone who has a bleeding disorder or is taking blood thinners should let the technician know in advance.
The doctor will receive the results from the lab and interpret them, then contact the person for a phone consultation or follow-up appointment.
The results of an ASMA test are either normal or abnormal.
Normal results indicate that a person has either none of the antibodies in their blood or only a trace amount.
These indicate that a person has higher amounts of ASMA in their blood.
The medical community considers results to be abnormal when the amount of ASMA in the blood sample corresponds to a titer of greater than 1:40.
These results can suggest that a person has:
- an autoimmune liver disease
- chronic hepatitis C infection
- infectious mononucleosis
- cancer of the breast or ovaries
- a melanoma
When ASMA levels are high, a doctor will likely request further tests to determine the cause. For example, they may also order an F-actin antibody test to check for antibodies that can indicate hepatitis.
If the results are inconclusive, a doctor may need to perform the test more than once. Also, different labs may return different values.
After determining why ASMA levels are high, the doctor will confirm and explain the diagnosis and develop a treatment plan.
The ASMA test is a low-risk procedure similar to any routine blood test.
The doctor's office sends the blood sample to a lab. A lab technician will analyze the levels of ASMA in the blood and return results.
The ASMA test can help a doctor to diagnose autoimmune disorders in the liver and other conditions.
If ASMA levels are high, the doctor may request additional testing before making a diagnosis and recommending a course of treatment.