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Antimitochondrial antibodies in serum
Last reviewed: 04.07.2025
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Antimitochondrial antibodies (AMA) are not normally detected in serum by the indirect immunofluorescence method; when using the ELISA method, normal values are less than 20 IU/ml; 20-25 IU/ml are borderline values.
Antimitochondrial antibodies are produced to antigens of the inner mitochondrial membrane. The antigen is a lipoprotein in structure, participating in the membrane transport functions. An increased titer of total antimitochondrial antibodies (1:160 and higher) is characteristic of primary biliary cirrhosis (in more than 90% of patients). A very small proportion of patients with primary biliary cirrhosis are AMA-negative. In secondary biliary cirrhosis, antimitochondrial antibodies are detected in low titers, or they are absent. Low titers of antimitochondrial antibodies can also be observed in chronic active hepatitis, chronic autoimmune hepatitis (up to 20% of cases), alcoholic or viral hepatitis.
Currently, there are 4 subtypes of antimitochondrial antibodies. For primary biliary cirrhosis, antibodies to mitochondrial antigens M-2 (a complex of enzymes on the inner membrane of mitochondria) are considered specific. The presence of antibodies against M-2 antigens can be detected by ELISA test systems. The diagnostic sensitivity of test systems for detecting primary biliary cirrhosis is 98%, specificity is 96%. The content of antimitochondrial antibodies M-2 over 25 IU/ml is considered elevated.
Along with anti-M2 antibodies, anti-M9, anti-M4 and anti-M8 antibodies are detected in primary biliary cirrhosis, in most cases simultaneously, which react with different epiotypes of the mitochondrial membrane. There is a relationship between the profile of antimitochondrial antibodies and the prognosis of primary biliary cirrhosis. Isolated detection of anti-M9 and/or anti-M2 in the blood serum correlates with a good prognosis of primary biliary cirrhosis. Progressive course of the disease is noted in patients with anti-M2, anti-M4 and/or anti-M8, in combination with an increased concentration of bilirubin in the blood serum.
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