Antimitochondrial Antibodies (AMA)
Last updated: October 8, 2014
Synonyms: AMA, Mitochondrial M2 antibodies
CPT Code: 83516
Description: AMA are antibodies to a variety of mitochondrial autoantigen complexes, designated M1–M9; M2 is the best characterized and most tested for antigen. Anti-Sp-100 antibodies are found in 25% of Primary Biliary Cirrhosis (PBC) patients and are highly specific for PBC.
Method: AMA is assayed with either indirect immunofluorescence (using rat kidney tissue substrate) or enzyme immunoassay (EIA) (also known as ELISA). EIA are done using pMIT3 (detecting antibodies against M2 via epitopes PDC-E2, BCOADC-E2 and OGDC-E2), gp210 or sp100 antigens. Older methods to detect AMA include complement fixation and radioimmunoassays.
Normal Values: Negative (titers = 1:20 or < 20 Units).
Abnormal in: AMA is not specific and may be seen in a variety of disorders.
—Primary biliary cirrhosis (PBC): Antibodies to M2 are sensitive for PBC because they are detected in 90% of patients with this disorder and are rarely seen in other diseases or normal persons. Titers in PBC typically exceed 1:160. Nearly half of PBC patients are ANA positive.
—Autoimmune hepatitis: AMA are found in 5%.
—Scleroderma: Subsets of patients with scleroderma (diffuse and limited) may have an overlap with PBC. In such patients, the AMA may be positive.
—Mitochondrial myopathy: A rare subset of patients demonstrate mild PBC and severe progressive myopathy and are positive for AMA.
—Other diseases: AMA have been detected in some patients with SLE, Sjögren’s syndrome, autoimmune thyroiditis, and myasthenia gravis.
Indications: AMA is most useful in the diagnosis of PBC and its differentiation from sclerosing cholangitis, a disease that can be clinically similar. It may be useful in distinguishing between PBC and extrahepatic biliary obstruction.