What does blood in the Stool look like?
Blood in the stool can be bright red, maroon in color, black and tarry, or occult (meaning not visible to the naked eye).
- Bright red blood seen in the stool, on toilet paper after wiping, or in the toilet bowl is referred to as hematochezia.
- Melana refers to stool that appears black or "tarry" (or sticky).
- Occult blood is blood not visible to the naked eye. In this case, the stool may look completely normal. Occult blood is typically identified during specific stool studies used to screen for colorectal cancer and to assess for gastrointestinal causes of blood loss or anemia.
What tests can be used to identify occult blood in my stool?
- The fecal immunochemical test (or FIT) uses antibodies to detect hidden blood in the stool that could be potentially coming from a cancer or tumor. It only detects human blood from the lower intestines making it is a more specific screening tool for colorectal cancer compared with the stool guiac test that many people may be more familiar with.
- The stool guiac test picks up blood arising from anywhere in the GI tract, making it less specific for colorectal cancer. For example, it might pick up blood arising from a bleeding stomach ulcer.
Why doesn’t all blood look the same in stool?
Generally, the closer the bleeding site is to the anus, the brighter red the blood will appear. Bleeding from the anus, rectum, and sigmoid colon (found on the left hand side of the abdomen) tends to be bright red, whereas bleeding from the transverse colon and ascending colon on the right hand side of the abdomen, located several feet away from the anus, tends to be darker red or maroon in color.
Melena occurs when blood is present in the colon for a long enough period of time that bacteria naturally present in the gut are able to break it down into chemicals that are black. Melena usually signifies bleeding from the upper gastrointestinal tract (for example, bleeding from ulcers in the stomach or small intestines).
Blood from the sigmoid colon and rectum usually does not stay in the colon long enough for bacteria to turn it black. As such, bleeding from these sites will tend to be brighter red. Rarely, massive bleeding from the right side of the colon, small intestine, or upper GI tract can cause a rapid loss of blood resulting in bright red rectal bleeding also, usually associated with other symptoms such as acute lightheadedness, dizziness and weakness.
Sometimes, bleeding from the gastrointestinal tract can be too slow to cause either bright red rectal bleeding or melena. In these cases bleeding is occult and the blood is only identified through laboratory testing. Occult bleeding is often associated with iron deficiency anemia.
What causes rectal bleeding?
Rectal bleeding can occur for many reasons.
Common causes include:
- Anal fissure (or tears)
- Solitary rectal ulcer syndrome.
Less common causes include:
- Anal or rectal cancer
- Colon cancer
- Inflammatory Bowel Disease (such as Crohn’s Disease, or Ulcerative Colitis)
- Pseudomembranous colitis (an inflammation of the colon caused by an infection with a specific type of bacteria known as C. diff)
- Ischemic colitis
- Rectal trauma, and
- Proctitis from radiation.
***Any rectal bleeding should prompt a complete evaluation by a trained medical provider. Rectal bleeding, whether perceived to be minor or not, can be a symptom of colorectal cancer, a type of cancer that if caught early can be treated effectively.