Blood in the Stool - Diagnosis

What was the diagnosis of blood in the stool?

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How is the cause of blood in the stool (rectal bleeding) diagnosed?

Patient history

Rectal bleeding is often diagnosed by history. The health care professional may ask questions about the circumstances surrounding the rectal bleeding including the color, the amount of bleeding, any associated symptoms and past medical history.

Medications and foods

A variety of medications and food can mimic blood in the stool. Iron supplements and bismuth (Pepto-Bismol, Kaopectate) can turn stool black, as can beets and licorice. Red food coloring and beets can turn stool a reddish hue.

Patients who take blood thinners (anticoagulation medications) are more prone to rectal bleeding. Examples of blood thinners include warfarin (Coumadin), enoxaparin (Lovenox), aspirin and other antiplatelet drugs including clopidogrel (Plavix), prasugrel (Effient) and rivoroxiban (Xarelto).

Diseases, alcohol, and location of bleeding

Patients with liver disease including those who abuse alcohol are at a higher risk for bleeding.

The color of stool may be a clue to the source of bleeding. Bright red blood in the stool often arises from the colon, maroon from the small intestine, and black from the upper GI tract. However, if the bleeding is brisk and the blood makes its way through the intestine quickly, there may not be sufficient time for the digestive juices to turn the stool color black.

Physical exam

Physical examination is important to assess the patient's stability. Vital signs are important and may include orthostatic vital signs, where the blood pressure and pulse rate are taken both lying and standing. In a patient with reduced blood volume, the blood pressure may fall, the pulse rate may rise, and the patient may become lightheaded and weak when standing. Palpation of the abdomen is performed to look for tender areas, masses or enlarged organs, especially the liver and spleen. Rectal examination is performed by inserting a finger into the rectum, with the purpose of feeling for a mass or other abnormality. The stool color and consistency may be examined when the finger is withdrawn. The anus also may be examined.

Blood tests

Blood tests may be considered if there is concern about the amount of bleeding or other associated diseases. A complete blood count (CBC) measures the number of red blood cells, white blood cells and platelets. Blood clotting tests include PT (protime), INR (international normalized ratio) and PTT (partial thromboplastin time). Depending upon the situation, other tests may be ordered to measure electrolytes, and kidney and liver functions.


If needed and depending upon where the health care professional believes the source of bleeding is located, procedures can be performed to look inside the GI tract. Anoscopy can be done in the office, where a lighted tube is inserted into the anus to inspect the first few inches of the anus and rectum.

Sigmoidoscopy and colonoscopy are outpatient procedures, often performed by a gastroenterologist or surgeon, where a flexible tube with a fiberoptic light is used to visualize the inside of the colon. A sigmoidoscopy looks at the lower 25 cm of the colon, while colonoscopy examines the entire colon from the anus to the cecum - where the small bowel enters the colon.

If the upper gastrointestinal tract is the suspected source, upper endoscopy is performed, usually by a gastroenterologist to examine the esophagus, stomach and duodenum, the first part of the small intestine.


X-rays may be helpful in evaluating the GI tract. Tests that can be considered include upper GI series, barium enema, small bowel studies and abdominal CT scans.

Return to Blood in the Stool (Rectal Bleeding)


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