Stool Color (cont.)
Melissa Conrad Stöppler, MD
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
In this Article
- What color is normal stool?
- What causes normal stool color?
- How do changes in bilirubin affect stool color?
- How does intestinal bleeding change stool color?
- What other things can cause changes in the color of stool?
- What are the symptoms of stool color changes?
- Find a local Gastroenterologist in your town
How do changes in bilirubin affect stool color?
Bilirubin travels with bile that is produced by the liver and then transported out of the liver by the bile ducts into the gallbladder, where it is stored until it is released into the intestines. (Bile is an important way for the liver to get rid of waste products such as bilirubin that are formed within the body.) As the bile and bilirubin pass through the intestines they are exposed to bacteria within the intestines. The bacteria can change the chemical nature of bilirubin, and this can change the color of stool.
If stool travels through the intestines at a normal speed, its color is a normal brown. Travel at a more rapid speed can result in chemical changes that may turn the stool green. Thus, green stool by itself is only a sign of a change of the speed with which stool is traveling and not necessarily a sign of disease. On the other hand, if the entry of bile into the intestines is blocked, for example, by a tumor of the bile ducts or pancreatic cancer, the stool becomes clay-colored. Clay-colored stool always is a sign of important disease.
How does intestinal bleeding change stool color?
One important internal process that can change the color of stool is bleeding into the intestines. The stool may turn black because of chemical changes to the hemoglobin in blood caused, in part, by the action of intestinal enzymes, particularly if bleeding is more rapid and there is a large amount of hemoglobin within the intestines. A color change to black also is more likely if the bleeding occurs in the upper intestine since there is more time for the chemical changes to the hemoglobin to take place as the blood travels through the intestines.
Stool that is black due to bleeding is also "sticky" (tarry) and smells bad. These latter characteristics help distinguish black stools due to internal bleeding from black stools due to the ingestion of iron or bismuth-containing medicines, for example, bismuth subsalicylate (Pepto Bismol).
On the other hand, bleeding that occurs lower in the intestines, particularly in the colon, is likely to cause red or maroon-colored stools since there is little time for chemical changes to the hemoglobin to take place.
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