Most rectal bleeding comes from the colon, rectum, or anus and can be associated with diarrhea. The color of the blood during rectal bleeding often depends on the location of the bleeding in the gastrointestinal tract. Generally, the closer the bleeding site is to the anus, the blood will be a brighter red. Thus, bleeding from the anus, rectum, and the sigmoid colon tend to be bright red, whereas bleeding from the transverse colon and the right colon (transverse and right colon are several feet away from the anus) tend to be dark red or maroon colored.
In some patients, bleeding can be black and “tarry” (sticky) and foul smelling. The black, smelly, and tarry stool is called melena. Melena occurs when the blood is in the colon long enough for the bacteria in the colon to break it down into chemicals (hematin) that are black. Therefore, melena usually signifies bleeding is from the upper gastrointestinal tract (for example, bleeding from ulcers in the stomach or the duodenum or from the small intestine) because the blood usually is in the gastrointestinal tract for a longer period of time before it exits the body.
Sometimes, bleeding from the gastrointestinal tract can be too slow to cause either rectal bleeding or melena. In these patients, bleeding is occult (not visible to the naked eye). The blood is found only by testing the stool for blood called fecal occult blood testing, FOBT in the laboratory. Occult bleeding has many of the same causes as rectal bleeding and may result in the same symptoms as rectal bleeding.
Scientists found adults with traces of blood in their faeces are nearly 60 percent more likely to face an early grave. A test to pick up traces of unseen blood in faeces is currently used to screen for bowel cancer in older people. But researchers now believe the faecal occult blood test (FOBT) may also be “the window to general health”.
Scientists at Dundee University tracked the survival of around 2,700 people whose FOTB test showed up as positive over a period of 16 years. Their survival rates were compared against more than 131,000 participants who tested negative for the invisible blood in their faeces. Subjects who scored positive for FOBT were almost eight times more likely to die from bowel cancer, than those who scored negative.
Researchers led by Professor Robert Steele also found a positive FOBT was linked with a 58 percent heightened risk of early death from all causes. Both findings remained true after gender, age, and deprivation were taken into account – four factors than can affect survival.
A positive FOTB test was linked most to a greater risk of death from circulatory, respiratory, digestive tract, neuropsychogical, blood and hormone diseases. It was also strongly linked with death from other types of cancer, excluding bowel, according to the study published in the journal Gut.
Evidence exists to show that many cancers and Alzheimer’s can develop against a background of chronic inflammation, among other conditions. They claimed half of bowel cancer screening patients who test FOTB positive don’t actually have the deadly disease. But a positive result could be used to alert those participants that they may be at risk of other life-limiting illnesses, the researchers said.
Professor Uri Ladabaum, of Stanford University, argued hidden stool blood ‘may be telling us more than we might have thought’. In a linked commentary to the study, he wrote: ‘If the eye is the window to the soul, is a faecal test the window to general health?’
Older age, increasing levels of deprivation, and male gender were associated with a greater likelihood of a positive test result. Prescriptions for aspirin or other drugs that boost the risk of digestive tract bleeds were also more likely to be associated with a positive test result.