Cholestatic pruritus is the sensation of itch due to nearly any liver disease, but the most commonly associated entities are primary biliary cholangitis, primary sclerosing cholangitis, obstructive choledocholithiasis, carcinoma of the bile duct, cholestasis (also see drug-induced pruritus), and chronic hepatitis C viral infection and other forms of viral hepatitis.
When this occurs, conjugated bilirubin and the waste products that usually would be cleared in bile reflux back into the bloodstream.
This is in contrast to primarily unconjugated hyperbilirubinemia which is the water-insoluble form that is bound to serum albumin; the liver has not had a chance to conjugate the bilirubin yet and can be caused either because too much unconjugated bilirubin is made (such as in massive hemolysis or ineffective erythropoiesis) or because too little is conjugated (Gilbert's disease or Crigler–Najjar syndrome).
It is thought that bile salts that deposit into the skin are responsible for the pruritus (itching) because the levels of bilirubin in the bloodstream and the severity of the pruritus does not appear to be highly correlated.
[2] Patients that have been administered bile salt chelating agents do report some relief, however, and patients that have complete liver cell failure (and therefore cannot make these products to begin with) do not have pruritus.