Could Black Stool Indicate Colon Cancer? Test Results - Gastroenterology and Hepatology

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Is it possible to have colon cancer?


Hello Doctor: I tend to be a bit anxious, so when I noticed my stool color was somewhat dark (not completely black), I became very worried and consulted a gastroenterologist.
The doctor indicated that I have hemorrhoids, but I still felt uneasy, so I underwent a fecal occult blood test and a CEA blood test.
Additionally, the gastroenterologist performed a digital rectal exam and an abdominal ultrasound, all of which showed no issues.
However, the fecal occult blood test returned a positive result (I had previously consumed blood rice, vegetables, and headache medication), while the CEA blood test was 1.1, which is normal.
Now, I occasionally notice a small amount of dark stool.
I would like to ask the doctor if the positive result from the fecal occult blood test is concerning, and whether those foods could really affect the test results.
Is there a possibility that it could be colon cancer?

Xiao Ling, 20~29 year old female. Ask Date: 2003/03/11

Dr. Yang Peizhen reply Gastroenterology and Hepatology


Hello! The stool color is somewhat black, and the fecal occult blood test is positive.
Some potential interfering factors (such as blood-containing meat, pig's blood, chicken blood, or duck blood) have been ruled out.
This usually raises suspicion for gastrointestinal bleeding; however, black stools typically indicate bleeding from the upper gastrointestinal tract (e.g., gastric or duodenal ulcers).
Bleeding from hemorrhoids or lesions in the lower colon (such as colorectal cancer) usually presents as bright red or dark red blood.
My recommendation is to first undergo an upper endoscopy to check for any lesions that may be causing the bleeding.
Next, a colonoscopy or lower gastrointestinal X-ray should be performed to rule out colonic lesions.
If necessary, small bowel imaging or angiography may be considered as a last resort.
Wishing you good health, Dr.
Yang Pei-Zhen, Gastroenterology, Taoyuan Hospital, Department of Health, Executive Yuan.

Reply Date: 2003/03/11

More Info


Black stool can indeed be a cause for concern, particularly when it comes to the potential for serious conditions like colon cancer. However, it's essential to understand that not all instances of black stool indicate a malignancy. The color and consistency of stool can be influenced by various factors, including diet, medications, and underlying health conditions.

In your case, the presence of black stool, especially if it is not completely black, can often be attributed to dietary choices. Foods such as black pudding (blood sausage), certain vegetables, and even iron supplements can lead to darker stool. Additionally, medications like non-steroidal anti-inflammatory drugs (NSAIDs) can irritate the gastrointestinal tract, potentially leading to bleeding, which may also manifest as black stool.

The positive result from your fecal occult blood test (FOBT) is indeed concerning, as it suggests the presence of blood in the stool, which can arise from various sources within the gastrointestinal tract. While hemorrhoids (or piles) can cause bleeding, they typically result in bright red blood rather than black stool. Black stool often indicates bleeding from the upper gastrointestinal tract, such as from peptic ulcers or gastritis, where the blood is digested and appears darker by the time it reaches the rectum.

Given that your carcinoembryonic antigen (CEA) levels were normal, this is a reassuring sign, as elevated CEA can be associated with certain cancers, including colorectal cancer. However, normal CEA levels do not completely rule out the possibility of cancer, particularly if there are other risk factors or symptoms present.

Considering your family history of colon cancer and your symptoms, it is prudent to follow up with further diagnostic evaluations. A colonoscopy is often recommended in cases of positive FOBT, especially for individuals with risk factors such as a family history of colorectal cancer. This procedure allows for direct visualization of the colon and rectum and enables the physician to take biopsies of any suspicious lesions.

In summary, while black stool can be alarming, it does not automatically indicate colon cancer. Dietary factors, medications, and benign conditions like hemorrhoids can all contribute to changes in stool color. However, given your positive FOBT and family history, it is essential to pursue further evaluation to rule out any serious conditions. Regular screenings, especially if you have a family history of colorectal cancer, are crucial for early detection and prevention. Always consult with your healthcare provider for personalized advice and to discuss the best course of action based on your specific situation.

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