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 only appreciable through specific laboratory analyzes.
The search for occult blood in the faeces represents an important screening test for colorectal cancer, recommended every year or every two years from 45/50 years of age. Like all screening methods, it should be emphasized that the search for occult blood in the stool has NO diagnostic significance, but simply identifies people at risk for this pathology and for intestinal polyps (which can be removed to prevent their possible transformation into malignant tumor). Therefore, if traces of blood are found in the patient's stool, this must be directed to diagnostic tests such as colonoscopy.In fact, we must not forget the long list of possible conditions that make the search for occult blood in the stool positive: duodenal and / or gastric ulcer, esophageal varices, ulcerative colitis, Crohn's disease, diverticulitis, anal fistulas, contamination of the sample with menstrual blood or urinary tract, 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 faeces 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 more important epidemiological studies, for example, the search for occult blood in the faeces showed - compared to individuals in the control group - a reduction in mortality equal to 33% when the test was performed every year and 21% when the test was performed every two years. The examination for fecal occult blood must be done even in the absence of disorders, since colorectal cancers often do not give any particular symptoms for years. Furthermore, if it is true that a positive data does not necessarily mean the presence of colon cancer, 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 contact 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; persistent sensation of rectal clutter after evacuation.
Preparation for the examination of research of occult blood in the faeces
Preparation for the exam is subject to the diagnostic techniques used by the analysis laboratory (Hemmocult or immunochemical tests).
Traditional techniques are based on the use of guaiac and exploit paper strips which, when treated with hydrogen peroxidase, develop a well-defined color in the presence or absence of heme (hemoglobin portion, contained in red blood cells, which binds oxygen) . To avoid false positives, in the days preceding the examination it is advisable to refrain from the consumption of raw or semi-raw red meats and cured meats of any kind, avoid 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, resulting in blood leakage). It is also important to brush your teeth gently, to avoid causing gum bleeding, and to follow a diet that is as rich as possible in dietary fiber.
With the latest generation tests it is no longer necessary to comply with these rules, since the search for occult blood in the stool uses specific antibodies directed against the protein portion (globin) of human hemoglobin. These tests, however, are only able to highlight the presence of occult blood from the colon and rectum, since globin does not pass the upper gastrointestinal tract unscathed (it is digested). These innovative histochemical investigations are generally used for their high specificity in screening tests for colon cancer / rectum, also due to the aforementioned independence of the 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 the patient respects the indications of the analysis center during the collection of fecal samples, generally based on the following recommendations:
- use the special sterile container equipped with an internal spoon;
- emit the feces in a container such as a chamber pot, avoiding mixing them with urine, toilet water or its detergents;
- collect the sample with the special spatula in three different points of the faeces, until about half of the container is filled in order to obtain a sample as homogeneous as possible;
- write the name on the label of the stool collection system;
- bring the container to the laboratory within a few hours, or, in the case of collecting more samples, store it in the refrigerator;
- do not perform the fecal occult blood test during menstruation, bleeding hemorrhoids, or when you lose blood in your urine.
