When a doctor suspects that a person may have primary biliary cirrhosis
A blood sample taken from a vein in your arm
This test measures whether antimitochondrial antibodies (AMA) are present in the blood. Moderate or high levels of AMA are strongly associated with primary biliary cirrhosis (PBC). PBC is an autoimmune disorder that causes inflammation and scarring of the bile ducts inside the liver, causing continual liver damage and blockage of the bile flow. It is found most frequently in women between the ages of 35 and 60. More than 90% of those affected by PBC will have high levels of antimitochondrial antibodies.
There are nine types of AMA (M1 – M9) of which M2 and M9 are the most clinically valuable. Antibodes to M2 target the pyruvate dehydrogenase (PDC) complex. The presence of the M2 type has been particularly evident in primary biliary cirrhosis, while the other AMA types may be found in other conditions and are not indicative of PBC.
In some laboratories, if testing for AMA is positive, then further tests for the M2 subtype is performed. Some laboratories have started to offer the AMA-M2 test instead of the AMA, which reduces the number of false positives from non-M2 antibodies.
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.
How is it used?
The AMA test is requested to help diagnose primary biliary cirrhosis (PBC). PBC is a serious condition in which the bile system in the liver are gradually destroyed. (For more about this disease, see the links listed under Elsewhere on the Web).
Other tests that may be requested include:
- Smooth muscle antibodies (SMA)
- Antinuclear antibodies (ANA)
- Levels of immunoglobulins (IgM, IgG, IgA)
- Liver function tests ( Bilirubin, Alkaline phosphatase, GGT, Alanine transaminase, Aspartate transaminase, Albumin)
- Prothrombin time
- C-reactive protein
- Liver biopsy
These tests can help in the diagnosis of PBC, and may distinguish it from other autoimmune conditions which case liver damage, and they may provide information about the degree of liver damage. The best test for diagnosis of PBC is a liver biopsy.
When is it requested?
The AMA or AMA-M2 test is requested when your doctor suspects that you have an autoimmune disorder such as PBC. You may have symptoms such as tiredness, jaundice and itchiness, but many patients affected with early PBC have no symptoms. The condition is often initially identified because a patient has elevated levels of enzymes which come from the liver and indicated that it is diseased. The enzyme alkaline phosphatase (ALP), is often elevated and this is found during routine blood tests.
An AMA or AMA-M2 test may be requested 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?
High levels of AMA or AMA-M2 in the blood are the most likely due to PBC. Low levels of AMA may also be present in patients with autoimmune hepatitis, liver or bile obstruction, and with infections such as syphilis or acute infectious hepatitis. AMA may also be present in patients with other autoimmune disorders related to PBC such as systemic lupus erythematosus, rheumatoid arthritis, Sjogren syndrome, scleroderma, and thyroiditis
Levels of AMA may be lower in children and in those with compromised immune systems. The level of AMA is not related to the severity of PBC symptoms or to a patient’s prognosis.
Is there anything else I should know?
By themselves, AMA and AMA-M2 can not be used to diagnose PBC, but in conjunction with other laboratory tests and clinical symptoms, a diagnosis of PBC can be made. When high levels of AMA or AMA-M2 are present and the doctor suspects PBC, a liver biopsy may be performed to look for the signs of primary biliary cirrhosis in the liver tissue. Imaging scans of the liver may also be used to look for bile duct obstruction.
About 50% of the cases of PBC will be discovered before the patient has noticeable symptoms.
What causes primary biliary cirrhosis (PBC)?
The cause of PBC is currently not known. It appears to be an autoimmune condition. It is not infectious and not inherited. It can occur in anyone at any age, but it is primarily seen in middle-aged women.
How fast does PBC progress?
I am M2 antibody positive, but have no symptoms and normal liver tests, what does that mean?
Up to 0.5% of the population are M2 AMA positive, only 10% of these will ever go on to develop PBC. PBC can only be diagnosed with the combination of abnormal liver function tests (alkaline phosphatase) and M2 AMA (with or without a liver biopsy).
If liver function is normal at baseline it could be repeated annually if the M2 antibody is confirmed on a second (repeat) test, with the reassurance that 90% of people will never develop problems.
On This Site
Tests: ANCA/MPO/PR3, Liver/Kidney microsomal antibody, Alkaline phosphatase (ALP), Alanine aminotransferase (ALT), Liver panel, Smooth muscle antibody (SMA), Antinuclear antibody (ANA)
Conditions: Autoimmune disorders, Liver disease, Hepatitis