[Medical Q&A] Gastrointestinal bleeding, how to judge the degree of bleeding from the color of stool?

Planner: Chinese Medical Association

Reviewer: Liu Huizhen, deputy chief physician of China Rehabilitation Research Center

When the digestive tract bleeds, the blood will mix with the digestive juices and food residues in the intestines, and after a series of chemical reactions, different colors of stool will be formed. These color changes actually reflect the amount, location and bleeding speed of the digestive tract bleeding.

When the amount of gastrointestinal bleeding is small, the color of the stool may not change significantly. This is because a small amount of blood is diluted by the digestive juice in the intestine, and the iron in the hemoglobin is sulfided in the intestine to form black ferrous sulfide, but this change may not be enough to change the overall color of the stool when there is a small amount of bleeding. However, if a fecal occult blood test is performed, a positive result may still be detected, indicating the presence of gastrointestinal bleeding. At this time, the amount of bleeding is usually 5 to 50 ml.

As the amount of bleeding increases, the color of the stool will gradually change. When the amount of bleeding reaches 50-100 ml, the stool begins to turn black and presents a tar-like luster. This color of stool is usually called "black stool" and is one of the typical manifestations of gastrointestinal bleeding. The appearance of black stool means that the amount of bleeding is relatively large and needs to be given sufficient attention by the patient.

If the amount of bleeding increases further, reaching 300-500 ml or even more, the color of the stool will become darker, showing tar black or dark red. At this time, the patient may not only have black stools, but also be accompanied by symptoms such as vomiting blood, nausea, and vomiting. The appearance of these symptoms often indicates that the gastrointestinal bleeding is already quite serious and requires immediate medical treatment.

It is worth noting that the location of gastrointestinal bleeding will also affect the color of stool. In the case of upper gastrointestinal bleeding (such as bleeding in the esophagus, stomach, and duodenum), the blood stays in the intestine for a long time and forms black ferrous sulfide after sulfidation, so the stool is mostly black or tarry. In the case of lower gastrointestinal bleeding (such as bleeding in the colon and rectum), the blood is close to the anus and is discharged from the body without being fully sulfided, so the stool may appear dark red or bright red.