Blood in the Stool: Bright Red or Black, Causes and Why to Be Examined

What it involves

MedlinePlus describes rectal bleeding as blood passing from the rectum or anus, which may show on the stool, on toilet paper or in the toilet and may be bright red. Black or tarry stools are a different sign, usually pointing to bleeding higher up in the digestive tract.

Who this is for

• Patients who see bright red blood on the paper, in the toilet or on the stool
• Patients whose stools are black and tarry
• Patients who assume hemorrhoids are the cause and have never had it examined
• Patients with belly pain, a change in bowel habits or unexplained weight loss along with bleeding

What to expect

• Questions about the color, how often it happens, pain, medicines and any change in bowel habits
• A physical exam focused on the abdomen and rectum
• Blood work for anemia and clotting, with referral for a colonoscopy or other scope where needed
• A plan for bowel care and follow-up, depending on what is found

What the color suggests

MedlinePlus says the color of the blood can hint at where it comes from. Black or tarry stools, called melena, are most often due to bleeding in the upper digestive tract, such as the esophagus, stomach, small intestine or right colon, because the blood is darkened as it is digested. Bright red or fresh blood usually means the source is the lower tract: the colon, rectum or anus. Less commonly, bleeding higher up can be brisk enough to appear bright red. Color is a clue, not a diagnosis.

Common and less common causes

MedlinePlus lists anal fissures, which are tears in the anal lining often caused by straining, hard stools or frequent diarrhea and which usually hurt; hemorrhoids, a common cause of bright red blood that may or may not be painful; proctitis; rectal prolapse; trauma or a foreign body; colorectal polyps; colon, rectal or anal cancer; ulcerative colitis and other types of colitis; intestinal infection; and diverticulosis. The hemorrhoids guide describes the most familiar cause, and the constipation guide covers the straining that can lead to fissures.

Why not simply assume hemorrhoids

MedlinePlus is direct: you should see your provider and have an exam, even if you think hemorrhoids are the cause of the blood in your stool. Hemorrhoids and more serious conditions can look the same from the toilet bowl, and a person cannot tell them apart by sight. The point of the exam is to find out, not to assume the harmless answer. That is especially true if bleeding comes with belly pain, mucus, or a change in the color or pattern of the stool.

What can mimic blood

MedlinePlus notes that eating beets or foods with red food coloring can make stools look reddish. In that case, a provider can test the stool with a chemical to check whether blood is actually present. It also says a small amount of blood in a child's stool is most often not serious, and the most common cause is constipation, though a child's provider should still be told. This page is written for adults. If you are unsure whether what you saw was blood, say so, and ask for it to be tested.

Signs that should not wait

MedlinePlus lists reasons to contact a provider: fresh blood in the stools, abdominal pain with blood or bloody mucus, a change in stool color, pain in the anal area while sitting or passing stool, incontinence, unexplained weight loss, and a drop in blood pressure that causes dizziness or fainting. If a person has dangerously low blood pressure or other signs of unstable circulation, it says they need immediate treatment. Call 911 for heavy bleeding with lightheadedness or fainting.

How the source is found

MedlinePlus says the provider takes a history and performs an exam focused on the abdomen and rectum, with a digital rectal exam, possibly an anoscopy, and sometimes a sigmoidoscopy or colonoscopy to look inside the colon with a camera on a thin tube. Blood tests may include a complete blood count, chemistries and clotting studies, and a stool test may check for infection. The colorectal cancer screening guide explains how routine screening differs from testing for bleeding.

Sources

• MedlinePlus — Rectal bleeding