Primary biliary sclerosis (PBC) is an autoimmune disease that causes destruction of intrahepatic bile ducts. PBC is often associated with other autoimmune disorders, particularly Sjogren syndrome. Anti-mitochondrial antibodies (AMA) are found in almost all patients with PBC and are considered the serological hallmark of the disease. AMA are useful diagnostically in distinguishing primary biliary cirrhosis from other types of chronic liver disease. They are present in approximately 95% of patients with primary biliary cirrhosis, but in only 7-30% of patients with chronic active hepatitis and cryptogenic cirrhosis. Patients with extrahepatic biliary obstruction, Wilson's disease, hemochromatosis, and alcoholic cirrhosis rarely have elevated titers. AMA are present in less than 1% of normal people and in less than 5% of patients with SLE, rheumatoid arthritis and other autoimmune diseases.
Traditionally, AMA have been detected with an immunofluorescent assay that looked for a mitochondrial pattern of staining of tissue sections. More recent studies have determined that AMA represent a heterogeneous mixture of antibodies to at least 9 different antigens, which are designated M1 - M9. The most predominant antibody reactivity in the sera of patients with PBC is directed against the pyruvate dehydrogenase enzyme complex (M2 antigen) located on the inner mitochondrial membrane. An enzyme immunoassay is now available for specific detection of antibodies against purified M2 antigen. The reference range will change as shown below.
Interpretation |
Current Method |
New Method |
Negative |
<1:20 |
<1.0 |
Weak positive |
1:20 - 1:80 |
1.0 - 1.3 |
Strong positive |
>1:160 |
>1.3 |
Specimen requirement will continue to be one red top or SST tube of blood.
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