Blood in Stool – All you need to know

Nicole Valentine
Nicole Valentine
June 27, 2023
min read
Technically reviewed by: 
Diagnox Staff
Blood in Stool – All you need to know

Finding blood in your stool can be a scary experience. While many causes of blood in stool are minor and require little to no treatment, blood in the stool can sometimes signify a serious problem. This blog will help you understand the difference between visible and occult blood in stool, the types of tests that can identify occult blood in stool, common causes of bleeding, and when to see a doctor.

Types of Blood in Stool

Blood in the stool is generally broken down into two categories — visible and occult. Visible blood can be seen in your stool, in the toilet, or on toilet paper after having a bowel movement. Occult blood isn't visible to the naked eye. It can only be detected with testing.

Visible Blood

Visible blood in stool ranges in color and appearance. It can be bright red or dark red. It can also be very dark or black and give your stool a tar-like appearance. The color of the blood can help point to where in your digestive tract it's originating from.

Visible blood can be caused by something as minor as hemorrhoids or as serious as colorectal cancer. It's important to track any bleeding you experience and report it to your doctor [1].

Occult Blood

If you have a small amount of blood in your stool, you may not be able to see it. Blood that can't be seen, known as occult blood, can only be detected through testing. If your doctor suspects occult bleeding or wants to test as a precaution, they can order a lab test. There are two types of tests your doctor might order:

  • Guaiac-based fecal occult blood test: You place a stool sample on a small card that is coated with a chemical called guaiac and send it to a lab or your healthcare provider. When there is blood in the stool sample, the card changes color due to the interaction of blood with guaiac.
  • Fecal immunochemical test: You put a small stool sample on a card or in a tube and send it to a medical lab — the lab tests for blood in the stool sample using an antibody that binds to hemoglobin.

Before taking a guaiac-based test, your doctor may tell you to avoid certain medications, supplements, and foods because they could cause false positive or false negative results. Before a fecal immunochemical test, you may also need to avoid taking certain medications, such as blood thinners, but you won't generally be required to make any dietary changes [2].

You can also test for blood in your stool at home without a doctor's order. To test your stool yourself, you'll need to purchase an over-the-counter fecal occult blood test kit. Some over-the-counter test kits show you your results in minutes. Others require that you send your stool sample to a lab for testing.

Tests like guaiac-based and fecal immunochemical can detect occult blood in the stool, ordered by doctors or done with over-the-counter kits, requiring precautions and sometimes dietary changes.

When to Test for Occult Blood in Stool

Your doctor may test for occult blood in your stool for a number of reasons, including [1], [3]:

  • Anemia (low red blood cell count)
  • Iron deficiency
  • Abdominal or rectal pain
  • Fatigue
  • Weight loss
  • Changes in bowel movements
  • Black stool

Testing for occult blood in your stool is also a screening method for colorectal cancer. Even if you have no symptoms, the Centers for Disease Control and Prevention (CDC) recommend that you start screening for colorectal cancer at age 45 [4]. Your doctor may recommend that you begin testing even earlier if they determine that you are at high risk [5].

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Causes of Blood in Stool

There are many possible causes of blood in stool, ranging from minor to life-threatening [1] [5]. Some of the common causes include:

  • Hemorrhoids: Swollen veins in the anus or lower rectum
  • Anal fissure: Tear or split in the anus
  • Rectal prolapse: Rectum that has descended through the anus
  • Diverticulitis or diverticulosis: Pouches in the lining of the digestive tract that may become inflamed or tear
  • Rectal polyps: Growths in the lining of the large intestine
  • Inflammatory bowel disease (IBD): Used in reference to Chron's disease or ulcerative colitis. IBD is categorized as chronic inflammation in the digestive tract
  • Ulcers: Open sores in the stomach or upper small intestine
  • Colorectal cancer: Cancer in the colon or rectum, which often starts as a polyp

When to See a Doctor

Finding blood in urine or stool is always something you should bring up with your healthcare provider. Blood in stool is sometimes benign, but it's difficult to determine the cause yourself, and some causes need prompt treatment. Even when the cause of bleeding appears to be obvious, something more serious could be going on. For example, hemorrhoids are a benign cause of bleeding that you can often treat easily at home. But rectal prolapse, which usually needs to be treated surgically, can be mistaken for hemorrhoids.

Be sure to keep a record of the bleeding, so you can inform your doctor of when it occurred and what it looked like. Even intermittent bleeding should be checked out. Your doctor may be able to determine the cause of bleeding based on your symptoms and a physical examination. Or they may order more testing to identify what's causing blood in your stool.

Always inform your healthcare provider if you find blood in urine or stool, as even seemingly benign causes may require prompt treatment. Keep a record of the bleeding and consult a doctor for proper evaluation, as further testing may be necessary to identify the underlying cause.

Accompanying Symptoms

There are some symptoms that can accompany blood in stool that indicate a serious problem. Get medical help immediately if you experience blood in your stool along with any of the following symptoms [2]:

The symptoms that can accompany blood in stool include sudden weight loss, persistent diarrhea or constipation, abdominal cramping, and fatigue or weakness.
  • Chest pain
  • Shortness of breath
  • Lightheadedness
  • Abdominal pain
  • Yellowing of skin or eyes
  • Nausea and vomiting
  • Fever
  • Difficulty swallowing


You should always inform your healthcare provider if you experience visible or occult blood in your stool. There are many causes of blood in stool, and some require medical intervention. Bleeding can also be the first indication of a more serious problem. If you or your doctor suspect that you might have occult blood in your stool, you can test a sample of your stool at home or send it to a lab for further testing. Fecal occult blood tests can also be used as a tool to screen for colorectal cancer.


1. Cleveland Clinic staff, “Rectal Bleeding,” Cleveland Clinic, Available Online here [Accessed June 2, 2023].

2. ASCO staff, “Fecal Occult Blood Tests,” American Society of Clinical Oncology, Available Online here [Accessed June 3, 2023].

3. Mount Sinai staff, “Stool Guaiac Test,” Icahn School of Medicine at Mount Sinai, Available Online here [Accessed June 3, 2023].

4. CDC staff, “What Should I Know About Screening?,” Centers for Disease Control and Prevention, Available Online here [Accessed June 3, 2023]

5. H.A. Dahl, “When to worry about blood in your stool,” The University of Texas MD Anderson Cancer Center, Available Online here [Accessed June 3, 2023].

About the Author
Nicole Valentine

Nicole Valentine is a blog and article writer with experience writing about a huge array of topics. She is passionate about sustainability, healthy living, and mindful parenting.

About the Reviewer
This blog was
Technically reviewed by: 
Diagnox Staff

Diagnox Staff consists of a multidisciplinary team of scientists, content writers, and healthcare professionals with an expertise to create and review high-quality, informative, accurate, and easy-to-understand content for both professionals and everyday readers. Our staff follows strict guidelines to ensure the credibility and authenticity of the information, reviewing them independently and verifying them by various scientific and technical sources to ensure accuracy. Our review team believes in delivering knowledge free from bias to improve public health and well-being.

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