Blood in Stool: Is It a Sign of Colorectal Cancer?

Seeing blood in your stool can be alarming, and it’s natural to worry about the worst. In most cases it comes from common, treatable conditions such as hemorrhoids, but it can also be an early warning sign of colorectal cancer. Because you can’t tell the cause just by looking, any blood in the stool is worth getting checked.

This article explains what colorectal cancer is, what different types of blood in the stool may mean, and how health screening can help find problems early.

What Is Colorectal Cancer?

Colorectal cancer is cancer that starts in the colon (large intestine) or the rectum, the final section of the digestive tract. Most cases begin as small growths called polyps on the inner lining of the bowel. Not every polyp becomes cancer, but some change slowly over many years, which is why finding and removing polyps early can prevent cancer from developing at all.

It is one of the most common cancers in the Philippines and worldwide. In its early stages it often causes no symptoms, so many people feel completely well while a polyp or small tumor is growing. By the time symptoms such as bleeding, changes in bowel habits, or abdominal pain appear, the disease may be more advanced. The good news is that colorectal cancer is highly treatable when caught early.

Types of Blood in Stool and What They May Mean

Not all blood in the stool looks the same, and its color and appearance can give doctors useful clues about where the bleeding is coming from.

Bright Red Blood 

Bright red blood usually points to bleeding in the lower part of the digestive tract, such as the rectum, anus, or lower colon. You may see it as streaks on the stool, on toilet paper, or as drops in the toilet bowl. It is most often caused by hemorrhoids or small anal tears (fissures), but it can also be a sign of polyps or colorectal cancer.

Dark, Tarry Stools 

This indicates bleeding from higher in the digestive tract, where blood has been mixed with the stool, giving it a dark, tar-like appearance.

Occult (Hidden) Blood

Sometimes bleeding is so slight that you cannot see it at all. This “occult” blood can only be found through a stool test. Slow, hidden bleeding over time can lead to iron-deficiency anemia, which may show up as tiredness, weakness, or paleness. Because it causes no visible change, stool testing is an important part of screening.

Since hidden blood can only be detected through chemical testing, a Fecal Occult Blood Test is highly recommended as part of health screenings. This simple step involves collecting two samples on two different days. Multiple collection is required since hidden blood is not always present in every bowel movement.

Other Symptoms to Watch Out For

Blood in the stool often appears alongside other symptoms of colorectal cancer, such as:

• Changes in bowel habits (diarrhea, constipation, or narrow stools)
• Persistent abdominal pain or cramping
• Unexplained weight loss
• Fatigue and weakness
• A feeling of incomplete bowel movements

Is Blood in the Stool Always Cancer?

No. Blood in the stool is a symptom, not a diagnosis, and most of the time it is caused by something other than cancer. Common causes include:

• Hemorrhoids: swollen veins in the rectum or anus, the most common cause of bright red blood
• Anal fissures: small tears in the lining of the anus, often from hard stools or straining
• Diverticulosis: small pouches in the colon wall that can sometimes bleed
• Inflammatory bowel disease (IBD): conditions such as Crohn’s disease and ulcerative colitis
• Polyps: non-cancerous growths that may bleed, and may become cancerous over time
• Infections or ulcers in the digestive tract

Still, you can’t tell the cause by looking. Bleeding from hemorrhoids and bleeding from a tumor can look the same, and having hemorrhoids does not rule out something more serious happening at the same time. For that reason, blood in the stool should always be checked by a doctor, especially if it:

• Lasts more than a few days or keeps coming back
• Comes with a change in bowel habits, abdominal pain, unexplained weight loss, or persistent tiredness
• Occurs in someone over 45, or with a family history of colorectal cancer or polyps

Seek urgent care if you have heavy bleeding, dizziness or fainting, or a rapid heartbeat along with bleeding.

How Doctors Confirm the Cause of Blood in Stool: Colonoscopy

While blood in stool is a concerning sign, it can also indicate other conditions like hemorrhoids, anal fissures, diverticulosis, or inflammatory bowel disease (IBD). That’s why proper medical evaluation is essential.

One of the most effective ways to confirm if bleeding is due to colorectal cancer is through a colonoscopy. This procedure involves inserting a thin, flexible tube with a camera into the colon to examine its lining for abnormalities. 

At Shinagawa Diagnostic, patients have the option of having a colonoscopy along will a comprehensive executive checkup with the VIP Shinagawa Dock. This package ensures that you get a complete picture of your digestive health and overall well-being and it also includes a CEA (carcinoembryonic antigen) blood test, a tumor marker that can provide additional information when colorectal cancer is a concern.