The diagnostic value of anti-mitochondrial antibodies, especially in primary biliary cirrhosis

Anti-mitochondrial antibodies (AMA) are present in sera of approximately 90-95% of patients with primary biliary cirrhosis (PBC) and, thus, constitute one of the most important diagnostic criteria for this disease. The major mitochondrial autoantigens have been identified, cloned, and sequenced and the immunological features of AMA, including their antigen specificities and epitopes, have been well characterized. In clinical laboratories, indirect immunofluorescence (IIF) microscopy is routinely employed for the detection of AMA mainly because of technical simplicity and cost effectiveness. However, IIF lacks both specificity and sensitivity, and in up to 10% of patients diagnosed with PBC based on standard diagnostic criteria, AMA cannot be detected by IIF. In some of these patients, AMA aredetectable by more sensitive techniques, such as enzyme-linked immunosorbent assays (ELISAs) or SDS-PAGE followed by immunoblotting. Nonetheless, there are patients whose sea are negative for AMA by any of these methods despite clinical, biochemical, and histological findings that are diagnostic for PBC. Some have argued that AMA-positive and AMA-negative PBC represent two distinct entities, but recent evidence supports the view that they are clinically and biochemically quite similar. The situation is further complicated by the fact that AMA, even those recognizing the major PBC autoantigens, are also present in a variety of other liver diseases. In addition, patients exhibiting the clinical, histological, and biochemical features of both PBC and autoimmune hepatitis, the so-called 'overlap syndrome,' are not uncommon. In conclusion, AMA status, though invaluable in establishing and confirming the diagnosis of PBC in > or =90% of PBC patients, is not sufficient by itself to allow the differential diagnosis of liver diseases. The choice of therapeutic regimen should, therefore, be based on a combination of serological, biochemical and histological findings, rather than AMA status alone.