Key Points about Bloody Stool

  • Bloody stool is caused by bleeding in one or more areas of the GI tract.
  • Signs of bloody stool may include bright red coating the stool, dark red mixed with the stool, or black stool--although blood may still be present in stool even if it is not visible.
  • Because the direct cause of bleeding may vary, it is important to first identify which area(s) of the GI tract from which the blood is originating.
  • Causes, symptoms, and treatment of bloody stool vary depending on the area of the GI tract that is affected.


Bloody stool is a relatively common gastrointestinal (GI) complaint that can be a symptom of several underlying conditions or can be temporary and relatively harmless. Bloody stool is caused by bleeding in one or more areas of the GI tract, and may be characterized by having bright red coating, having dark red mixed throughout, or appearing black.

While bloody stool may not necessarily be signaling a serious problem, it is important to consult a doctor as soon as possible to rule out potentially harmful underlying causes of the bleeding.

Your doctor can perform a range of diagnostic tests to identify the source and any underlying cause of bleeding.

Bloody stool causes

Bloody stool is caused by bleeding in one or more areas of the gastrointestinal (GI) tract, which includes the esophagus, stomach, small intestine, large intestine or colon, rectum and anus.

The direct cause of bleeding may vary. It may come from a small area such as an ulcer on the lining of the stomach, or from a large area such as inflammation throughout the colon.

Bloody stool risk factors

Risk factors for bloody stool include having:

  • Hemorrhoids
  • Crohn’s disease
  • Ulcerative colitis
  • Constipation
  • Irritable bowel syndrome

Bloody stool symptoms

Blood may be present in stool even when it is not visible. Symptoms of bloody stool may include:

  • Bright red blood coating the stool
  • Dark blood mixed with the stool
  • Black stool
  • Bright red blood in vomit
  • Vomit that looks like coffee grounds

Bloody stool complications

Surgery is often necessary to control active, severe or recurrent bleeding when other methods such as endoscopy are not successful.

Bloody stool diagnosis

When searching for the cause of bloody stool, it is important to identify the source of the bleeding within the GI tract.

Your doctor will conduct a complete history and physical examination. Your doctor may also perform a blood count to look for anemia, and to assess the extent and chronicity of the bleeding.

The following diagnostic procedures may also be used to identify the source of bleeding:

  • Endoscopy — The endoscope is a flexible instrument that can be inserted through the mouth or rectum to detect lesions and confirm the presence or absence of bleeding. This instrument allows the doctor to see into the esophagus, stomach, duodenum, colon and rectum. The doctor can use this tool to collect small samples of tissue, to take photographs, and to stop the bleeding.
  • Computed Tomography (CT or CAT) Scan — A CT scan allows doctors to create and view images of the GI tract to look for possible sources of bleeding.
  • Angiography — This technique uses dye to highlight blood vessels and is most useful in situations when the patient is bleeding acutely, as dye leaks out of the blood vessel and identifies the site of bleeding. In some cases, doctors can use angiography to inject medicine into arteries that may stop the bleeding.

Bloody stool treatment

Doctors may treat GI bleeding with the following methods:

  • Endoscopy — Endoscopy is the most common therapeutic procedure for treating GI bleeding. For upper GI tract bleeding, doctors often inject chemicals into the area through a needle on the endoscope that will control bleeding.
  • Cauterization — A doctor may cauterize the source of bleeding and its surrounding tissue with tools attached to the endoscope.
  • Laser therapy — This technique may be used in some situations.

When to seek care

Most often, bloody stool is not due to colon cancer or another serious condition. Because it is not possible to know the cause of bloody stool without an examination, however, anyone who notices blood in their stool should consult a doctor to determine whether an examination is needed.

Next Steps

After controlling the bleeding, measures may be taken to treat the underlying cause and prevent future bleeding. Your doctors may:

  • Prescribe medication
  • Treat any ulcers
  • Remove polyps from the colon
  • Remove hemorrhoids

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