Is Rectal Bleeding a Sign of Cancer?

This page is for anyone who has seen blood from the bottom and wonders if it could be cancer. It explains how color and amount change the urgency, the common causes, and what tests may follow.

Two details decide almost everything about how fast you should be seen. What color was the blood, and how much of it was there?

Bright red blood on the paper, streaked on the stool, or turning the water pink usually comes from close to the exit. Black or very dark blood has traveled farther and been digested along the way. That means bleeding higher up.

A large amount of any color is urgent regardless of source.

MedlinePlus is clear. Call 911 or go to the nearest emergency room if:

• There is a lot of blood in your stool. Bleeding that will not stop, toilet water that turns red, or large clots all count.
• You have black, tarry stools.
• You vomit blood, or material that looks like coffee grounds.
• You feel lightheaded or dizzy from the bleeding.
• You have chest pain or trouble breathing.
• You have severe belly pain along with bleeding.

Do not drive yourself. MedlinePlus notes that massive bleeding from the gut can be dangerous or even life threatening.

This tier catches people out, because the amount can look small.

Black, tarry stool is on the 911 list above, because it can be a sign of bleeding higher up in the gut. MedlinePlus says to contact your provider right away if you notice blood or changes in the color of your stool. So call your doctor the same day if:

• Your poo is dark red.
• You have bloody diarrhea.

One caution from the NHS: stool can look very dark from iron tablets, or from foods like licorice and blueberries. A doctor can test to sort out which it is, so do not assume either way.

For a small amount of bright red bleeding that settles, MedlinePlus says to contact your provider to discuss the next step. Book an appointment with your primary care doctor, and mention if you also have:

• Poo that has been softer, thinner or longer than normal.
• A lot of pain around the bottom.
• A pain or lump in your tummy.
• More tiredness than usual.
• Weight loss for no reason.

The NHS also says to see a doctor straight away if a child has blood in their poo.

The NHS pairs patterns with likely causes:

• Bright red blood with pain when pooing, an itchy bottom and lumps: piles.
• Bright red blood with pain, often after constipation: an anal fissure.
• Bright red blood with no pain: sometimes a side effect of anticoagulants or aspirin, or fragile blood vessels in the gut.
• Bloody diarrhea with cramps and bloating: inflammatory bowel disease.
• Bloody diarrhea with slime, feeling sick: a tummy bug.
• Blood with slime and a change in bowel habit: bowel polyps or early bowel cancer.

Diverticular bleeding, infections and sexually transmitted infections round out the list.

The NHS states it plainly. Bleeding from the bottom is sometimes a sign of bowel cancer, it is easier to treat when found early, and that is why it is important to get it checked.

NCI groups the signs of colon cancer together:

• Blood in the stool that is either bright red or very dark.
• A change in bowel habits.
• A feeling that the bowel does not empty completely.
• Stools that are narrower than usual.
• Abdominal discomfort.

Anal cancer can also bleed, often with itching, pain or a lump at the anus. Both are worth an exam rather than a guess.

The NHS describes what happens at the appointment. A doctor may check your bottom with a gloved finger, ask for a stool sample for testing, and refer you to a specialist for tests.

From there the usual options are:

• A blood count, to see whether you have lost iron over time.
• A stool test for hidden blood.
• Flexible sigmoidoscopy, which looks at the lower bowel.
• Colonoscopy, which looks at the whole colon and can remove polyps.
• CT scanning if a fuller picture is needed.

Screening history matters here. The US Preventive Services Task Force recommends colorectal cancer screening for adults aged 45 to 75.

Describe the blood exactly. On the paper, in the bowl, or mixed through the stool are three different answers.

Note how many episodes, over how long, and whether it hurt. Record your bowel habit over recent weeks, your weight, your energy, and any blood-thinning medicine. Colorectal Cancer Screening explains the test options if you are due.

• NHS — Bleeding from the bottom (rectal bleeding)
• MedlinePlus — Gastrointestinal bleeding
• MedlinePlus — Bloody or tarry stools
• National Cancer Institute — Colon Cancer Treatment (PDQ)
• US Preventive Services Task Force — Colorectal Cancer: Screening