PBC is diagnosed using a combination of blood tests and, less frequently, liver biopsy.
In blood test terms the key features are cholestatic biochemistry (elevated alkaline phophatase and or gamma)-GT and PBC-specific autoantibodies (anti-mitochondrial antibody or anti-PDH on ELISA) or PBC-specific anti-nuclear antibodies.
On liver biopsy the diagnostic feature is the classical bile duct lesion typically seen in the context of liver granuloma.
When all three features (biochemistry, antibody and liver biopsy findings) are present the diagnosis is classified as “definite”. When two out of three are present (usually in the setting where biopsy has not been done) the diagnosis is regarded as “probable”. Elevated serum IgM levels are an additional useful feature (and very common in PBC) but don’t form part of the standard diagnostic combination.