The stool has a number of different substances including wastes, indigestible foods like fiber, mucus, water and bacteria. Blood should not be present, even though some of the components of blood cell breakdown such as bilirubin, may be present. When blood is seen in the bowel movement or detected with medical tests then it has to be investigated further because it is a cause for concern.
How does blood enter bowel movement?
Blood enters the bowel movement somewhere along the course of the digestive tract. This means it can be from bleeding in the mouth, throat, esophagus, stomach, small intestine, large intestine, rectum or anus. Sometimes bowel from the genitalia or urinary tract may be mistaken for blood in bowel movement.
When there is bleeding high up in the digestive tract like from the esophagus or stomach then the blood becomes degraded as it travels down the bowels to be passed out with stool. This may cause the stool to look dark and tarry which is known as melena.
When there is bleeding lower down in the digestive tract like bleeding from the colon or rectum then the blood may be noticed on the stool, in the toilet water or when wiping after a bowel movement. This fresh red blood in the bowel movement is known as hematochezia.
Fecal Occult Blood Test
Often the blood is not visible to the naked eye and only detected when diagnostic investigations are conducted on a stool sample. The fecal occult blood test (FOBT) is a technique to detect blood in the stool. Even small amounts of blood may be detectable with this test.
Irrespective of the location, blood in the bowel movement means that there is bleeding somwhere in the digestive tract. This is also known as the gastrointestinal tract or simply as the gut. There are various different conditions which may cause this gastrointestinal bleeding. Bowel movement blood is just a symptom of these conditions.
WARNING: Blood in the stool should always be taken seriously. While it may be due to many conditions that are acute and not of a serious nature, sometimes this bleeding in the bowel movement can be a sign of life-threatending conditions like colorectal cancer. Always consult with a doctor if rectal bleeding persists or if other severe symptoms are also present. A prompt diagnosis of colorectal cancer is important for a better outcome.
Read more on rectal bleeding.
Causes of Bowel Movement Blood
Any bleeding anywhere in the gut may give rise to bowel movement blood, whether visible as fresh red blood in the stool, black tarry stools or blood only detected upon diagnostic tests like the fecal occulat blood test (FOBT). Although even bleeding from the mouth can be the cause of bowel movement blood, the more likely causes that are important to consider include the following.
Visible blood upon wiping, in the bowel movement and sometimes in the toilet water is often due to hemorrhoids (piles). This is a condition where the rectal veins become swollen and inflamed. It is usually painful, causes burning and itching in the anus and rectum as well as tenesmus (urging to pass stool even after a bowel movement). However, sometimes hemorrhoids may present with no other symptoms apart from blood in the bowel movement.
Anal fissures are tiny tears that occur in the delicate lining of the anus. It occurs when passing large stools, with constipation or chronic diarrhea. The tears heal quickly if there is no further irritation. The blood in the bowel movement is usually accompanied by pain while passing stool and thereafter as well as itching and burning in the area, similar to hemorrhoids.
A bleeding peptic ulcer is one of the more common causes of blood loss from the upper part of the gut. These ulcers mainly occur in the duodenum or stomach but can also arise in the esophagus. The bleed is usually slow and persistent but can become severe if there is a perforation (hole).
Inflammatory Bowel Disease
Inflammatory bowel disease (IBD) is another common cause of blood in the bowel movement. The gut wall becomes inflamed and ulcerated with bleeding at some sites. Crohn’s disease can occur anywhere in the gut so the bleeding may even arise in the upper gut. Ulcerative colitis is usually isolated to the colon and rectum where there may be blood loss.
Varices are abnormal enlargements of veins mainly in the esophagus or stomach. These veins can burst and cause blood to leak out into the gut. When it does rupture, there can be massive blood loss. It is most commonly associated with liver disease like cirrhosis. Apart from blood in the bowel movement, sometimes there is also bloody vomiting (hematemesis).
Diverticula (singular ~ diverticulum) are abnormal pouches that form in the colon. These pouches can sometimes bleed often causing visible blood to appear in the bowel movement. It tends to arise suddenly. The exact cause of diverticulosis (formation of diverticula) is unclear but is more frequently seen in people over the age of 40 years and may be associated with chronic constipation.
Cancer anywhere in the gut can lead to bleeding. This may not be obvious higher up the gut but visible blood in the bowel movement along with changes in bowel habit and unintentional weight loss should raise the concern about colorectal cancer. It is among the more common and deadliest of cancers.
Read more on what is colon cancer.
Benign (non-cancerous) tumors may also be responsible for bleeding in the gut. This is mainly seen with colonic polyps, although some of these polyps may be precancerous. However, most colon polyps do not cause any symptoms and are discovered during diagnostic investigations like a colonoscopy.
Gastrointestinal infections (gastroenteritis, colitis) are another possible cause of bleeding in the bowel movement. It typically presents with diarrhea which may be bloody. This is more often seen with bacteria (bacillary dysentery) such as an infection with Shigella, Salmonella, Campylobacter and Aeromonas spp. It may also be seen in amoebic dysentery caused by Entamoeba histolytica.