Faecal occult blood

We speak of "occult blood in the faeces" when the excrements have rather small traces of blood, such as not to be visible to the naked eye but appreciable only through specific laboratory analysis.

The search for occult blood in the stool is an important screening test for colorectal cancer, recommended annually or biennially starting at 45/50 years of age. As with all screening methods, it should be noted that the search for occult blood in the faeces has NO diagnostic significance, but simply identifies those at risk for this pathology and for intestinal polyps (which can be removed to prevent their possible transformation into malignant tumor).

Therefore, in the event that traces of blood were found in the patient's faeces, this must be directed towards diagnostic tests such as colonoscopy. We must not forget the long list of possible conditions that make positive the search for occult blood in the feces: duodenal and / or gastric ulcer, esophageal varices, ulcerative colitis, Crohn's disease, diverticulitis, anal fistulas, contamination of the sample with menstrual blood or urinary, hemorrhoids, anal fissures, inadequate diet in the days preceding some types of tests. Although devoid of diagnostic significance, the search for occult blood in the stool remains a particularly valuable investigation for making an early diagnosis, which in turn results in a significantly better prognosis (greater chances of survival). According to the results of one of the most important epidemiological studies, for example, the search for occult blood in the faeces showed - compared to the individuals in the control group - a reduction in mortality of 33% when the test was performed every year and on the 21st % when the test was performed every two years. The examination for fecal occult blood testing should also be done in the absence of disorders, since colorectal cancers often do not give any particular symptoms for years. Moreover, if it is true that a positive datum does not necessarily mean the presence of a colon tumor, the opposite situation is also possible, since the pathological process can produce intermittent bleeding. Therefore, even if a recent examination has had a negative result, it is advisable to consult your doctor in the presence of the following disorders: persistent changes in bowel habits; presence of blood in the stool evident to the naked eye; sensation of persistent rectal bulk after evacuation.

Preparation for the fecal occult blood test

Exam preparation is subject to diagnostic techniques used by the analysis laboratory (Hemmocult or immunochemical tests).

Traditional techniques are based on the use of guaiac and exploit strips of paper that, when treated with hydrogen-peroxidase, develop a well-defined color in the presence or absence of EME (hemoglobin portion, contained in red blood cells, which binds oxygen) . To avoid false positives, in the days before the exam it is advisable to refrain from eating raw or semi-raw red meats and cold cuts of any kind, avoiding particularly rich sources of vitamin C (foods, drugs and supplements), alcohol and anti-inflammatory medicines such as Aspirin © (which could damage the mucous membrane of the stomach, with consequent leakage of blood). It is also important to brush your teeth gently, to avoid causing gum bleeding, and follow a diet as rich in dietary fiber as possible.

With the latest generation tests it is no longer necessary to comply with these rules, since the search for occult blood in the faeces uses specific antibodies directed against the protein portion (globine) of human hemoglobin. These tests, however, are only able to highlight the presence of occult blood coming from the colon and rectum, since globine does not pass unharmed the upper gastrointestinal tract (it is digested). In general, these innovative histochemical investigations are used for high specificity lotus in colon / rectal cancer screening tests, also due to the already mentioned independence of results from possible haemorrhages of the initial tracts of the digestive tract (gastric and duodenal ulcers, esophageal varices etc).

In order to guarantee a correct result it is important that during the collection of fecal samples the patient respects the indications of the analysis center, generally based on the following advice:

• use the special sterile container with an internal spoon;
• emit the faeces in a container type chamber pot, avoiding mixing them with urine, with the water from the toilet or with its detergents;
• collect the sample with the appropriate spatula in three different points of the feces, until about half of the container is filled so as to obtain a sample as homogeneous as possible;
• write the name on the label of the faeces collection system;
• take the container to the laboratory within a few hours, or, if more samples are collected, store it in the refrigerator;
• do not perform the occult blood test in stool during menstruation, in the presence of bleeding hemorrhoids or when blood is lost with urine.