What does the antimitochondrial antibody mean?

In a prospective survey positive antimitochondrial antibodies have been detected in 69/4200 (1.64%) of all sera submitted to a routine immunology laboratory. Of the 69, only nine patients had uniquivocal primary biliary cirrhosis, six others had chronic active hepatitis, 10 had abnormal liver function tests without evidence of primary biliary cirrhosis, while the remaining 44 had no clinical or biochemical evidence of liver disease. Outside the context of liver disease antimitochondrial antibodies were observed with similar frequency in patients with autoimmune disorders as in other conditions. It was not possible to distinguish primary biliary cirrhosis from patients without liver disease by antibody titre or by immunoglobulin subclass. The positive antimitochondrial antibody patients without liver disease were uniformly distributed throughout the city of Sheffield, in contrast with the marked clustering of cases of primary biliary cirrhosis. We conclude that, in the absence of clinical liver disease, the antimitochondrial antibody test alone (as detected by routine immunofluorescent techniques) does not appear to be a specific screening test for primary biliary cirrhosis. While we cannot exclude the possibility that the autoantibody indicates a predisposition to develop primary biliary cirrhosis, further prospective studies are needed to determine which patients will progress in this manner. The possibility that environmental factors may be implicated cannot be discounted.