Stool Color (cont.)
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.
What other things can cause changes in the color of stool?
Another internal process that may change the color of stool but that is less
common than bleeding is pancreatic disease. The pancreas secretes enzymes into
the intestines that help with the digestion of fat, protein, and carbohydrates.
When pancreatic enzymes are not present in the intestine, fat is not fully
digested. If the content of undigested fat is high enough, stool may become a
yellowish color. The stool also appears "greasy" and smells bad. The most common
pancreatic diseases that cause this are
pancreatic tumors that block the
pancreatic duct through which the enzymes reach the intestines and chronic
pancreatitis, usually
due to damage from excessive ingestion of alcohol, that destroys the ability of the
pancreas to make enzymes. If there is both blood and undigested fat in the
stool, the stool may become silver.
Several ingested substances can change the color of stool. Iron and
bismuth-containing medications, for example, Pepto Bismol, turn the stool black. Beets and possibly some other red vegetables and fruits can turn
stool a reddish color. Food dyes used for coloring foods also may color the
stool.
Last Editorial Review: 4/1/2008
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