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Hematologist, oncohematologist

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Causes of bloody feces

Alexey Kryvenko, medical expert
Last reviewed: 04.07.2025

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The diagnostic value of the occult blood test for early detection of colon cancer depends on the volume of bleeding from the tumor. On average, blood loss from tumors of the cecum and ascending colon is 9.3 ml/day (from 2 to 28 ml/day). With localizations distal to the hepatic flexure of the intestine, blood loss is significantly less and is 2 ml/day. This difference may be due to the larger size of tumors in the proximal colon. Blood loss from an adenomatous polyp averages 1.3 ml/day, regardless of its location.

A positive reaction of feces for occult blood is possible in many diseases:

gastric ulcer and duodenal ulcer;
primary and metastatic tumors of the esophagus, stomach, intestines, duodenal papilla;
intestinal tuberculosis, nonspecific ulcerative colitis;
helminth invasions that injure the intestinal wall;
dilation of the veins of the esophagus in liver cirrhosis and thrombophlebitis of the splenic vein;
Rendu-Osler disease with localization of bleeding telangiectasias anywhere on the mucous membrane of the digestive tract;
typhoid fever (in patients with typhoid fever with positive results of the reaction for occult blood in the feces, macroscopic bleeding occurs significantly more often than with negative results; although severe bleeding is possible without previous occult bleeding);
when blood from the mouth and larynx enters the digestive tract, when the lips are cracked, when blood is accidentally or intentionally (for the purpose of simulation) sucked out of the mouth, and when it flows in cases of nosebleeds;
blood from hemorrhoids and anal fissures entering the feces;
menstrual blood entering the stool.

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