Sector: Hormone 1
Transport: at 2-8˚c, -20˚c
Storage: 5 day at 2-8˚c for longer time at -20˚c
Test Name: Anti smooth muscle Ab
Normal Range: Up to 1.10
To help diagnose autoimmune hepatitis and distinguish it from other causes of liver injury or disease
When a patient has hepatitis or a liver disorder that the doctor suspects may be due to an autoimmune-related process
A blood sample taken from a vein in your arm
This test looks for the presence (and if present the level) of smooth muscle antibodies (SMA) in the blood. Antibodies usually protect the body against infecting organisms such as bacteria and viruses. However, antibodies which are produced against parts of the body rather than outside organisms are known as autoantibodies and can cause disease rather than protect against it. SMA are autoantibodies produced by the body’s immune system that are directed against proteins of the smooth muscle. These ‘cytoskeletal’ proteins form a framework within a cell and support its structure. Smooth muscle differs from skeletal muscle that we use for walking, lifting, and other movements e.g. biceps, triceps muscles. Smooth muscle is present in the walls of blood vessels, the bowel and bladder, amongst other locations. F-actin is one specific cytoskeleton protein which SMA may target. Testing for autoantibodies to F-actin is performed in some laboratories. It is thought that its performance is similar, or possibly better, than SMA itself. The clinical utility of the anti-actin test has yet to be established, and it is not widely used in the UK.
The presence of SMA is strongly associated with autoimmune hepatitis (more specifically type 1 autoimmune hepatitis). It may also be seen much less commonly in other forms of liver disease such as primary biliary cirrhosis, and in viral infections (e.g. hepatitis B). Usually, higher levels of SMA are seen in autoimmune hepatitis compared with other causes.
Autoimmune hepatitis is an acute or chronic inflammation of the liver caused by the immune system mistakenly attacking the cells of the liver. It is not the direct result of other causes such as a viral infection, drug, toxin, hereditary disorder, or alcohol abuse. It can lead to liver and, in some cases, to liver failure.
Autoimmune hepatitis can be found in anyone at any age, but about 80% of those affected are women.
How is the sample collected for testing?
A blood sample is taken by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.