Background & Aims: Liver biopsy has been largely replaced by less invasive measurements applied to mathematical models in defining the prognosis of patients with primary biliary cirrhosis (PBC). The need for liver biopsy in the diagnosis of patients with positive antimitochondrial antibodies (AMAs) in the setting of biochemical cholestasis remains uncertain. This study was undertaken to determine which variables indicate the need for liver biopsy in patients with positive AMA and suspected PBC. Methods: A total of 3198 patients that were tested for AMA in 1999 and 2000 were identified. Of these, 198 (6.2%) were AMA positive. Forty-two patients were excluded because of unavailable laboratory data or liver biopsy specimens. Data on the remaining 156 patients were analyzed to determine which variables among patients with positive AMA with and without a histopathologic diagnosis of PBC indicate the need for liver biopsy. Results: In 131 of 156 (84.6%) patients, a diagnosis of PBC was established by liver biopsy. The histological diagnosis of PBC was associated with a cholestatic biochemical profile (alkaline phosphatase [AP] >1.5 times the upper limits of normal [ULN] and aspartate aminotransferase [AST] <5 times ULN) in 112 of 131 (85.5%) patients. The combination of AP >1.5 times the ULN and AST <5 times the ULN yielded a 98.2% positive predictive value of PBC diagnosis on liver biopsy in AMA-positive subjects. These results were corroborated by cross-validation in an independent set of patients. Conclusions: In patients with positive AMA, a cholestatic biochemical profile (AP >1.5 times the ULN), and absence of markedly elevated AST (<5 times the ULN), liver biopsy is rarely required to establish the diagnosis of PBC. Liver biopsy would be beneficial to establish the diagnosis of PBC in only a minority of AMA-positive patients with AP <1.5 times the ULN or AST >5 times the ULN.
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