OncoCare Cancer Centre

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Patient Education

Colon Cancer Presenting as Blood in the Stools
Colon Cancer Presenting as Blood in the Stools

Seeing blood in the stools is distressing and frightening to a lot of people. The uncertainty of where it comes from, and whether there is an underlying serious illness such as cancer adds to the fear. This concern is magnified when there is a large quantity of blood, when it is fresh red and particularly when the patient is not able to explain it away. The blood can occur during or after a bowel movement or passing motion, or it could just be noticed on the tissue paper cleaning oneself in the toilet.

Blood can come from the upper intestinal tract such as the oesophagus and stomach, to the colon and anus. Bleeding that happens in the upper digestive tract may make stool appear black and tarry from mixture with digestive juices.  Bleeding from the lower gastrointestinal tract may look more bright red. There are many potential causes of blood in the stools.

  • Anal fissure – a tear in the anal lining

  • Haemorrhoids or piles

  • Polyps or cancer

  • Colitis or inflammation related to infection or inflammatory bowel diseases (such as Crohn’s disease or ulcerative colitis).

  • Diverticular disease -small pouches in the wall of the colon which can bleed particularly when they become infected.

  • Angiodysplasia – abnormal and fragile blood vessels in the intestines.

  • Ulcers in the upper gastrointestinal tract – an open ulcer or sore in the lining of the stomach, duodenum, or the upper end of the small intestine.

  • Oesophageal problems such as dilated veins in the oesophagus related to chronic liver diseases.

  • Other less common conditions including blood vessel, blood clotting disorders


The passage of blood per rectum is not uncommon and is often attributed by patients to haemorrhoids or piles. However, it is not something to be ignored especially in Singapore where colorectal cancer was the most common cancer among men and the second most common cancer among women in the period 2007-2011.  At OncoCare Cancer Centre, Singapore, we do see many colorectal cancer patients presenting with blood in the stools initially.

The type and amount of the bleeding as well as the age of the patient are important details in the initial assessment of the bleeding. Rectal bleeding should be evaluated. The exact incidence for rectal bleeding is not known but the incidence increases with age.


When a patient has bleeding per rectum (bleeding PR), initial workup should include a history and physical examination.

Important related history and symptoms to note include:

  • The quantity and nature of bleeding. As a general rule, fresh, bright red blood is usually from the lower gastrointestinal tract.  In colorectal cancer, blood loss may also be minimal or not visible to the human eye or termed occult blood.

  • Weight loss

  • Change in bowel habit (both frequency of defecation and type of stool) , some patients with colorectal cancer can have constipation or diarrhoea

  • Tenesmus refers to the feeling of needing to pass motion or incomplete emptying. It can be a symptom of cancer of the rectum. This is due to the tumour in the rectum causing such a sensation.

  • Anal symptoms such as a mass or persistent pain.

  • Family history of colorectal cancer or polyposis (such as familial adenomatous polyposis (FAP), hereditary nonpolyposis colon cancer (HNPCC)). Such families should be evaluated closely since the known risk for related family members is higher than the general population.

  • Medical history, trauma, use of aspirin or other medications, previous radiation treatment. Prior radiotherapy can cause a condition of bleeding that can happen many years later from the treatment. Patients might have had radiation treatment for prostate, cervix, endometrium or other cancers of the pelvis in the past.

A general examination including blood pressure, pallor, weight loss, abdominal masses is usually done. Perianal and rectal examination can be done. A proctoscope can sometimes identify the source of haemorrhoid bleeding.

Further Evaluation

Full blood counts can be done to check for anaemia which could mean bleeding from a cancer in the bowels. If the anaemia is due to blood loss, it is usually iron deficiency anaemia, and iron levels in the  blood can be checked easily. In the end, if colorectal cancer is suspected, colonoscopy is performed to confirm the diagnosis by getting a biopsy and sometimes it is able to stop the bleeding in some situations.  In situations where the bleeding is massive, resuscitation, fluids and transfusion is administered before definitive surgical/ interventional procedures are planned. Continue reading below…

Colorectal cancer can be successfully treated when detected early. (Further information on colorectal cancer)


“Expert knowledge means better care for cancer”


Written by:

Dr Peter Ang Dr Benjamin Chuah
MBBS (Singapore) MBBCH
MMed (Int Med) BAO (Ireland)
MRCP (UK) MRCP (United Kingdom) FRCP (Edinburgh)
FAMS (Medical Oncology) FRCP (Medical Oncology)