Pale Stool, Dark Urine & Biliary Obstruction: Mechanism

Created for the National Cancer Institute, http://www.cancer.gov

Catabolism of hemoglobin leads to the release of heme, which converts to biliverdin and then to unconjugated bilirubin in the reticuloendothelial system.

Since unconjugated bilirubin is lipid-soluble, the renal system cannot eliminate it. Instead, it is transported to the liver, where it is converted to conjugated bilirubin, a water-soluble form that becomes part of bile.

Mechanism: Biliary obstruction, often caused by gallstones, can lead to jaundice and dark urine, while causing pale stools and possibly pruritus due to bile acid deposits in the skin. The pale stool results from the inability of bile to reach the intestinal tract and the dark urine from renal filtration of bilirubin.

References

1. Lorenz JM. Management of Malignant Biliary Obstruction. Semin Intervent Radiol. 2016 Dec;33(4):259-267. doi: 10.1055/s-0036-1592330.
2. Pavlidis ET, Pavlidis TE. Pathophysiological consequences of obstructive jaundice and perioperative management. Hepatobiliary Pancreat Dis Int. 2018 Feb;17(1):17-21.
3. Liu JJ, Sun YM, Xu Y, Mei HW, Guo W, Li ZL. Pathophysiological consequences and treatment strategy of obstructive jaundice. World J Gastrointest Surg. 2023 Jul 27;15(7):1262-1276. doi: 10.4240/wjgs.v15.i7.1262.