Antimitochondrial Antibody and AMA M2
A blood sample drawn from a vein in your arm
Antimitochondrial antibodies (AMA) are autoantibodies that are strongly associated with primary biliary cholangitis (PBC), formerly called primary biliary cirrhosis. This test detects and measures the amount (titer) of AMA in the blood.
Primary biliary cholangitis is a chronic autoimmune disorder that causes inflammation and scarring of the bile ducts inside the liver. It is a slow-progressing disease that causes worsening liver destruction and blockage of the bile flow. Blocked bile ducts can lead to a build-up of harmful substances within the liver and may eventually lead to permanent scarring (cirrhosis). PBC is found most frequently in women between the ages of 35 and 60. About 90-95% of those affected by PBC will have significant titers of antimitochondrial antibodies.
AMA are autoantibodies that develop against antigens within the body. There are nine types of AMA antigens (M1 – M9) of which M2 and M9 are the most likely to cause illness (clinically significant). The presence of the M2 type of AMA has been particularly evident in PBC, while the other types may be found in other conditions. Some laboratories offer the AMA-M2 as a more specific test for PBC.
For more information on PBC, see the links in the Related Content section.
How is the test used?
The antimitochondrial antibody (AMA) test or the AMA-M2 test may be ordered to help diagnose primary biliary cholangitis (PBC).
Other tests that may be ordered include:
- Smooth muscle antibodies (SMA)
- Antinuclear antibodies (ANA)
- Alkaline phosphatase (ALP)
- IgM level
- Prothrombin time (PT)
- C-reactive protein (CRP)
These tests often help detect PBC, distinguishing it from other autoimmune conditions causing liver damage, and may be useful in helping to predict whether a person may need a liver transplant.
When is it ordered?
- Itching (pruritus)
- Abdominal pain
- Enlarged liver
Many of those affected with early PBC do not have any symptoms. The condition is often initially identified because a person has abnormal results on a liver panel (elevated liver enzymes), especially alkaline phosphatase (ALP).
An AMA or AMA-M2 test may be ordered along with or following a variety of tests that are used to help diagnose and/or rule out other causes of liver disease or injury. These causes can include infections, such as viral hepatitis, drugs, alcohol abuse, toxins, genetic conditions, metabolic conditions, and autoimmune hepatitis.
What does the test result mean?
A high AMA or AMA-M2 level (titer) in the blood indicates that the most likely cause of symptoms and/or liver damage is PBC. The level of AMA is not related to the severity of PBC symptoms or to a person's prognosis.
A negative AMA or AMA-M2 means that it is likely that a person's symptoms are due to something other than PBC, but the result does not rule out the condition. About 5-10% of those with PBC will not have significant amounts of AMA or AMA-M2.
Is there anything else I should know?
By themselves, AMA and AMA-M2 are not diagnostic of PBC, but in conjunction with other laboratory tests and clinical symptoms, the diagnosis of PBC can be made. A liver biopsy may be performed to look for characteristic signs of PBC in the liver tissue and to confirm the diagnosis but is not always necessary. Imaging scans of the liver may also be ordered to look for bile duct obstructions.
About 50% of the cases of PBC will be discovered before a person has noticeable symptoms.
What causes primary biliary cholangitis (PBC)?
The cause is currently not known. It is not infectious and not inherited, although an increased susceptibility to develop autoimmune disorders may occur in some families. It can occur in anyone at any age, but it is primarily seen in middle-aged women.
How fast does PBC progress?
The course and severity of PBC is difficult to predict. Many people will have no or few symptoms for many years. For more information, consult with your healthcare practitioner and see the links in the Related Pages section.
Can I have an AMA or AMA-M2 test done in my healthcare practitioner's office?
If I have AMA, will the antibodies ever go away?