Stage 4 of primary biliary cholangitis (PBC) is biliary cirrhosis, which is severe, permanent scarring and damage to the liver. In this stage, the liver tissue regenerates, forming regenerative nodules of various sizes, and the number of bile ducts decreases.

Stage 1. There's inflammation and damage to the walls of medium-sized bile ducts. Stage 2. There's blockage of the small bile ducts. Stage 3. This stage marks the beginning of scarring. Stage 4. Cirrhosis has developed. This is permanent, severe scarring and damage to the liver.

I believe that is the last most serious stage