PBC is diagnosed by serum alkaline phosphatase levels greater than 1.5 times the upper limit of normal and typically normal serum total bilirubin levels. Serum aspartate (AST) and alanine (ALT) aminotransferase levels are typically less than five times the upper limit of normal. Serum antimitochondrial antibody is present in 90% to 95% of patients. For patients with undetectable serum antimitochondrial antibody levels, a liver biopsy is required for diagnosis.