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The stool occult blood test, also known as stool occult blood test, is a test that assesses the presence of small amounts of blood in the stool that may not be visible to the naked eye and, therefore, serves to detect the existence small bleeds in the digestive tract that may indicate ulcers, colitis or even bowel cancer.
The examination of occult blood in stool is usually requested by the doctor as a way to investigate the occurrence of bowel cancer, especially in people who have a family history, to investigate the cause of anemia or to assist in the diagnosis of inflammatory bowel changes, such as disease Crohn's disease and colitis, for example.
How to prepare for the exam
In order to do the occult blood test in the stool, it is important that the person follows some recommendations from the doctor during the collection period, which is usually 3 days, as some factors can interfere with the result. Thus, it is recommended:
- Avoid consumption of foods such as radish, cauliflower, broccoli, beets, beans, peas, lentils, chickpeas, corn, olives, peanuts, spinach or apples;
- Avoid taking drugs that irritate the stomach, such as anti-inflammatory drugs or aspirin, for example, as they can cause bleeding and result in a false positive, in addition to supplements with vitamin C and iron;
- Do not perform the exam less than 3 days after the menstrual period;
- Do not perform a search for occult blood in the stool when bleeding from the gums or nose is seen, as the person may swallow the blood and be eliminated together with the stools;
If the collection of feces is done in any of these situations, it is important to inform the laboratory so that it is taken into account when analyzing the result. However, in most cases it may be necessary to repeat the test to confirm the result.
The fecal occult blood test is considered a screening test, allowing evidence of the presence or absence of inflammatory bowel diseases to be identified without having to perform more expensive and invasive procedures.
Nevertheless, the diagnosis of the disease should not be made based only on the result of the occult blood test, despite having high sensitivity, and a colonoscopy should be recommended, which is considered the "gold standard" test for the diagnosis of inflammatory diseases. intestinal infections, including colorectal cancer. Understand how colonoscopy is performed.
See in the following video how to collect the stool for the exam:
Understanding the Exam Result
Possible results for the stool occult blood test are:
- Negative occult blood in the stool: it is not possible to identify occult blood in the stool, with a low risk of gastrointestinal changes;
- Positive occult blood in the stools: indicates the presence of occult blood in the stools and, therefore, the doctor recommends carrying out complementary tests, mainly colonoscopy, the cause of the bleeding and starting the appropriate treatment.
In case of a positive or negative result with some changes, the doctor may request to repeat the test to confirm the result or perform a colonoscopy according to the person's clinical history.
False positive results are those in which the presence of blood is detected, through the test, but which does not represent the patient's condition. This type of result can happen in people who do not prepare properly with regard to diet, have had gingival or nasal bleeding, have used drugs that cause irritation of the gastric mucosa, or have had the collection a few days after the menstrual period.
In some cases of negative results, the doctor may still request a colonoscopy if the patient is at high risk of developing colon cancer to ensure that there are no changes, as, although it is rare, there may be cancer without bleeding.
See other problems that can cause changes in stools.
Main causes of occult blood in stool
The presence of blood in the stool is usually indicative of intestinal changes, the main ones being:
- Benign polyps in the intestine;
- Hemorrhoids;
- Ulcers in the stomach or duodenum;
- Ulcerative colitis;
- Crohn's disease;
- Diverticular disease;
- Colorectal cancer.
Thus, in order to identify the correct cause of the presence of blood in the stool, it is common that after the occult blood test the doctor orders a colonoscopy or an endoscopy, especially when the bleeding is not caused by hemorrhoids. These two exams consist of the introduction of a thin tube with a small camera at the tip, which allows you to observe the inside of the intestine and stomach to identify possible injuries, facilitating the diagnosis.
See even more about the main causes of blood in the stool.