What it measures
Smooth muscle antibodies (ASMA) are antibodies against proteins in smooth muscle, such as actin. They are found in many people with autoimmune hepatitis, a condition in which the immune system attacks the liver. Low levels can also appear for a time after viral infections.
Why people test it
- Measured when liver tests are abnormal and autoimmune hepatitis is being looked into.
- Part of an autoimmune liver screen, with antinuclear and mitochondrial antibodies.
Typical range
The result is reported as positive or negative, often with a titre (how far the sample can be diluted and still show the antibody). Labs use their own methods and cut-offs, and the report shows the lab's wording.
Finger-prick or vein?
A finger-prick sample is often enough, as antibody tests need only a small amount of serum. A vein sample is taken where a lab or a larger panel needs more blood.