When to take a stool test for occult blood: indications, preparation and types of research. Feces for occult blood: purpose and preparation for analysis Occult blood in stool decoding

A fecal occult blood test is a diagnosis of the presence of occult blood in the stool using sensitive chemical elements. During the interaction between the research sample and chemical substance oxidation and color change occur. Except chemical reactions V modern medicine The immunoenzyme method is used. A stool sample is used for testing.

Why is analysis needed?

It is known that already in the early stages of the disease, colon cancer causes mild, constant bleeding. This is due to the fact that the formations that appeared in the process of exposure cancer cells, bleed, and this blood enters the colon. But there are cases when it is not possible to detect blood in the stool with the naked eye (that is, hidden blood). With such symptoms, specialists refer patients for diagnosis of occult blood in the stool.

A positive test for occult blood occurs in cases where the patient has diseases of the gastrointestinal tract. They cause damage to the mucous membrane of the human body, and a small amount of blood is released into the lumen of the stomach and intestines. This process occurs with a stomach ulcer or duodenum, ulcerative colitis, Crohn's disease, helminth infestations or polyps.

Cancers damage the mucous membrane of the gastrointestinal tract already in the first stages of the disease. Therefore, if you suspect cancer a positive result appears.

This technique is of particular importance in the study of colon oncology, since when cancers in this part of the intestine, chronic hidden bleeding appears in the first stages of the development of the disease.

In addition, a positive result in the occult blood test can be caused by bleeding from the nose, gums and oral cavity. Also, the test for occult blood is positive for varicose veins of the esophagus, erosive esophagitis, hemorrhoids and other diseases.

The reliability of an occult blood test with a positive result is highest if it is repeated. But if the study shows a negative result, then one should not exclude the presence of ulcers and cancer of the gastrointestinal tract in a person. Receipt efficiency positive result depends on the subsequent laboratory diagnostics, because stool occult blood testing alone cannot be used to establish the disease.

Preparing for analysis

An occult blood test may be prescribed by: medical specialists, as: gastroenterologist, therapist, oncologist, surgeon and doctor general practice. Preparation for analysis is as follows:

• 3 days before testing the sample, it is necessary to exclude from the diet all meat and fish dishes, as well as vegetables and fruits containing peroxidases and catalases (for example, cauliflower, cucumbers, horseradish, apples, spinach, white beans);
• stop taking it seven to ten days before medicines, such as aspirin (acetylsalicylic acid), laxatives, non-steroidal anti-inflammatory drugs, as well as drugs containing iron and bismuth;
• It is forbidden to give enemas;
• If you undergo X-ray diagnostics, you can donate stool no earlier than two to three days later;
• It is recommended to take a sample for analysis after three consecutive bowel movements, and the material for research is collected from various places in the stool.

The diagnostic specimen (fresh stool) should be placed in a plastic container with a tight-fitting lid. Biological material is collected after spontaneous defecation, and care must be taken to ensure that no urine gets into the stool. Sample for research medical laboratory transported on the same day within two to three hours.

Indications for analysis

Your doctor may prescribe a stool test for occult blood if you have the following symptoms:

• the presence of abdominal pain, nausea, heartburn and vomiting;
• the presence of constant mushy bowel movements, constipation, loss of weight and appetite, increased temperature;
• presence of cancer digestive organs to further eliminate invisible bleeding of the gastrointestinal tract;
• the presence of helminths (for diagnosing disorders of the mucous membranes of the gastrointestinal tract);
• the presence of diseases such as ulcerative colitis, intestinal tuberculosis, Crohn's disease.

False positive and false negative test results

U absolutely healthy person with the correct digestive tract process, the occult blood test shows a negative result. When examining a biological sample of a healthy person, only fibers from vegetables and fruits can be detected, which cannot be digested by the intestines. Therefore, testing stool for occult blood with a negative result is considered normal.

The analysis also shows a negative result in the presence of colon polyps in the human body. This is due to the fact that this technique misses almost 20% of cases of development colorectal cancer and polyps. If the test shows a negative result, but there is a high risk further development oncology of the large intestine, prescribed additional diagnostics(colonoscopy or flexible sigmoidoscopy).

Often, a stool occult blood test shows a false positive result. In most cases, this is due to improper preparation before collecting the biological sample. Also, a false positive test result can occur with bleeding of the gums and nose, during which a person absorbs a small amount of blood. It passes into the stomach and from there into stool samples. A false positive result is also observed in cases where a person has periodically recurring bleeding.

Fecal occult blood test

Fecal occult blood test – laboratory test stool, aimed at identifying hemoglobin. The fecal hemoglobin test is performed as a screening for minor internal bleeding. Determination of occult blood in feces is used to diagnose pathological processes in the gastrointestinal tract, when varicose veins veins of the esophagus, intestinal polyps, stomach and duodenal ulcers or hemorrhagic syndrome. For analysis, feces are collected in a sealed container. The most common research methods are immunochemical or guaiac test. In healthy adults, a stool occult blood test should be negative. The duration of the study ranges from 1 to 4 working days, depending on the method.

Fecal occult blood testing is considered a “laboratory alternative” to colonoscopy. If the patient has opened heavy bleeding from some part of the gastrointestinal tract, then first of all the color of the stool changes, which can be determined even by eye. If there is bleeding from the lower intestine (such as the rectum), the blood in the stool will be bright red. When the upper gastrointestinal tract (esophagus, stomach or small intestine) bleeds, the stool becomes tarry. In this situation, the patient should be provided with urgent health care. Whenever minor bleeding due to injury to the gastrointestinal mucosa, the coloring and consistency of stool do not change, and red blood cells are determined during microscopy. If microscopic examination does not reveal red blood cells, and symptoms indicate the presence of hidden bleeding, then a stool test for occult blood is required.

When this test is carried out regularly, the detection of malignant tumors of the large intestine on last stage decreases by 45%. In healthy patients, no more than 0.5 ml of blood per day can normally be excreted in the stool. Fecal hemoglobin usually does not lead to changes in the color of stool and is not detected by macroscopic methods. When bleeding is less than 45 ml, the stool test for occult blood becomes positive, so the test is carried out to diagnose polyps, ulcers, diverticula or tumors of the gastrointestinal tract on initial stage. This test is widely used in gastroenterology, proctology and oncology to determine pathological processes in the gastrointestinal tract.

Indications

A fecal occult blood test is prescribed during a medical examination (for patients of pre-retirement age, preferably once every 2 years), if a tumor is suspected, as well as for people suffering from helminthiasis, polyposis, gastric erosion or nonspecific ulcerative colitis. If instrumental method If a neoplasm of the gastrointestinal tract (benign or malignant) is diagnosed, the patient is advised to test stool for occult blood to exclude minor bleeding. Symptoms for which testing is ordered include discomfort during bowel movements and false urges, intestinal dyspepsia, abdominal pain, diarrhea, sudden weight loss, restless sleep, weakness, fever, changes in the structure of stool, the presence of foam and mucus in the feces. Hidden bleeding often appears clinical symptoms hypochromic or microcytic anemia, therefore, if there are signs of anemia, not only instrumental examination(gastroscopy and colonoscopy), but also a stool test for occult blood.

Preparing for analysis

Collection of stool for analysis for occult blood is carried out in the morning (in women no earlier than 7 days monthly cycle). Before collecting biomaterial, it is important to stop taking iron-containing drugs, bismuth, anticoagulants and laxatives for several days. It is not recommended to do an enema before the test. A stool occult blood test is performed 1-3 days before instrumental studies(sigmoidoscopy, irrigoscopy or colonoscopy). 12 hours before collecting feces, it is important to adhere to a special diet - exclude liver, meat dishes and iron-containing foods (peppers, apples, greens, beans). You can use buckwheat, rice porridge, potatoes, butter, bread, dairy products. It is important to deliver the container with feces to the laboratory immediately after collecting the biomaterial. Storage in the refrigerator (at temperatures from +4 to +80C) for several hours is allowed. Feces are collected after spontaneous defecation, and it is important to ensure that no urine gets into the container (feces are collected from 3 different places).

To detect fecal hemoglobin, an immunochemical test or benzidine and guaiac tests are used. With the guaiac method, feces are applied to paper, after which hydrogen peroxide and a guaiac reagent are added. The principle of testing samples is that heme in hemoglobin manifests itself as a peroxide (it instantly destroys the structure of hydrogen peroxide). As a result, benzidine or guaiac (depending on what is used) quickly oxidizes and turns a different color. If there are traces of blood in the feces, the paper changes color within a few seconds.

The immunochemical fecal occult blood test uses antibodies to intact human globin and hemoglobin. The advantage of this technique is considered to be increased specificity and sensitivity (98-99%) in the diagnosis of bleeding in the area of ​​direct and colon. However, the immunochemical test is not sensitive to bleeding from the upper gastrointestinal tract, where globin is quickly digested, so in this case the guaiac test is predominantly used. The period for performing a stool occult blood test is from 1 to 4 days, depending on the chosen method.

Normal values

Normally, in healthy people, hemoglobin is absent in the analysis of stool. At quantification negative result – from 0 to 50 ng/milliliter. Repeated testing is sometimes required to confirm reference values. The absence of hidden blood in the stool does not 100% exclude the presence of ulcers or neoplasms of the gastrointestinal tract in the patient, so it is important that the test results are evaluated together with other studies.

Positive result

The main reason positive reaction feces for occult blood is considered to be a violation of the integrity of the mucous membrane of the gastrointestinal tract and the development of minor bleeding in patients due to injuries to the nasal mucosa, stomatitis, periodontal disease, gastric ulcers, ulcerative colitis, hemorrhoids, erosive esophagitis or intestinal tuberculosis. Primary and secondary neoplasms, colon cancer cause bleeding and inflammation of the gastric and intestinal mucosa in the first stage of the disease, so these pathologies are also the cause of a positive reaction in the stool test for occult blood. Vascular network on the surface malignant tumor small intestine or a colon polyp has a fragile structure, so it is easily injured during the act of defecation. In this case, a small amount of blood enters the stool, which cannot be visually determined.

Treatment of abnormalities

Fecal occult blood testing is considered common medical research, thanks to which it is possible to diagnose bleeding from different segments of the gastrointestinal tract, including tumor processes at the initial stage. When receiving test results, it is important to immediately contact your treating specialist: oncologist, gastroenterologist, proctologist, surgeon, pediatrician, therapist, dentist. A fecal occult blood test does not provide information about the location and cause of bleeding, so if the test is positive, the patient may be recommended a colonoscopy or endoscopy (the procedures will reveal the source of inflammation, cancer, erosion, polyp, hemorrhoids or intestinal diverticula). The doctor also prescribes additional tests: coprogram, stool culture for dysbacteriosis, OAC with leukocyte formula and ESR, fecal examination for Giardia, scraping for enterobiasis. To adjust indicators when re-analysis It is important to adhere to a special diet and refrain from taking medications (vitamin C, aspirin, bismuth and iron preparations).

Examination of feces for occult blood is one of the laboratory tests that makes it possible with a high degree of probability to diagnose internal bleeding in one of the sections of the gastrointestinal tract. Particular attention is required when preparing for a stool occult blood test, since if it is absent or performed incorrectly, false positive results may be obtained.

Indications for the purpose of analysis

Examination of stool for blood hidden in it is prescribed for the following patient complaints:

• Constant/recurrent abdominal pain;
• frequent symptoms of dyspeptic disorder - nausea, vomiting, heartburn;
• regular diarrhea;
• unexplained weight loss.

Testing stool for blood present in its composition is prescribed to confirm the diagnosis, for example, peptic ulcer or erosive gastritis. The overall goal of the analysis is to identify hidden damage to the mucous membranes of the stomach or intestinal tract.

Types of tests

If there are bleeding areas of the mucosa, blood may be present in a person's excrement. If the site of bleeding is the stomach or duodenum, then the stool becomes dark red in color. When the surface of the large intestine is damaged, they become scarlet. But it is not always possible to see blood impurities in a person’s stool. Very often, small ulcers bleed only periodically.

Laboratory testing of stool for occult blood can determine even the minimal amount of hemoglobin contained in it.

The study is performed in two ways:

• Gregersen method (benzidine test);
• immunochemical test.

The Gregersen test is quite informative, but only if the patient has thoroughly prepared

Gregersen's technique allows you to detect even the minimum concentration of hemoglobin. This is both an advantage and a disadvantage of the method. Benzodine colors iron molecules blue, but it reacts with both human and foreign hemoglobin (present in meat).

The immunochemical method is more accurate. Its significant drawback is that it takes quite a long time. Test results will be received only two weeks after submitting the material for research. Therefore, in most cases, stool testing is prescribed using the Gregersen method.

Preparing for the Gregersen test

To get the most reliable results, you need to properly prepare for stool donation. The recommendations will be as follows:

1. A week before the planned delivery, it is necessary to stop taking medications such as laxatives, bismuth- and iron-containing drugs, and non-steroidal anti-inflammatory drugs. It is prohibited to use acetylsalicylic acid and medications containing it.
2. It is necessary to avoid administering rectal suppositories.
3. Enema is prohibited.
4. Before testing stool for occult blood - two days before the test - you need to exclude any instrumental tests of the gastrointestinal tract. During the study, the mucous membrane may be accidentally damaged. Released blood may cause false positive results.
5. A few days before collecting excrement, you should stop brushing your teeth. Even a small amount of blood released when the gums are damaged can enter the stomach. And this hemoglobin can also negatively affect the final result.

Before the test is performed, the patient will be advised to follow a special diet. Its duration is 72 hours.

The main point of preparing for the test is strict adherence to the diet.

The patient's diet should completely exclude foods high in iron. The collection of stool must be preceded by refusal:

• from apples;
• cucumbers;
• white beans;
• spinach;
• horseradish;
• cauliflower;
• meat and fish dishes;
• offal;
• green vegetables.

Ideally, in order not to make a mistake with the menu, doctors recommend adhering to a dairy diet during the days of preparation for donating stool. The diet may also include:

• potato;
• bread;
• porridge (with the exception of buckwheat, oatmeal, egg, lentils, peas).

Collection of stool for research

Even careful preparation will be completely useless if the biological material is collected incorrectly.

There are special containers for transporting feces to the laboratory - they are sterile and guarantee the biological purity of the collected excrement

How to pass feces correctly? To obtain material suitable for research, you must follow the following recommendations:

1. A sterile container must be used to collect excrement. It can be purchased at any pharmacy. The set includes a jar with a lid and a special spoon.
2. First you need to empty your bladder. Then place an oilcloth in the toilet.
3. After bowel movements, it is necessary to take three portions of feces from different places.

The material must be delivered to the laboratory within the next three hours. It cannot be stored.

False results

Failure to follow the preparation rules before donating stool may result in erroneous results. They can be either false positive or false negative.

The main reason for false-positive tests indicating the presence of internal bleeding is improper preparation.

False positive results are quite common. The reason is a person’s disdainful attitude towards the preparatory stage. In this case, the test shows a high hemoglobin content in the absence of internal bleeding. Just one apple eaten a day before the delivery of biological material can distort the final results.

Proper preparation for examining stool for occult blood in many cases allows you to avoid a very unpleasant colonoscopy procedure. The technique involves examining the intestines by inserting equipment through the anus.

It is known that from a blood test we can determine whether a patient has chronic anemia. Its positive confirmation in the form of a low content of red blood cells - erythrocytes, a decrease in hemoglobin levels indicates the presence of blood loss. Moreover, bleeding can be sluggish, periodic and hidden. And when it is not possible to establish obvious sources of bleeding, it was invented special analysis stool for blood.

Taking a test, conducting a study, how to test feces for occult blood?

Indications for analysis

The analysis is needed to determine whether there is damage to the gastrointestinal tract. If the integrity of the mucous membrane of at least one organ is compromised, this will be visible in the results.

The reasons for the analysis may be:

1. Serious illnesses intestines.
2. Ulcer.
3. Colitis.
4. Polyps.
5. Anemia.
6. Poor appetite.
7. Abnormal stool.
8. A sharp change in weight downward.
9. Frequent constipation.
10. Heartburn.
11. Acute pain in the abdominal area.
12. Constant nausea.

In addition, feces for occult blood are taken if there is a suspicion of cancer or benign neoplasm.

Let us remind you that you can get a referral for analysis from a surgeon, therapist, oncologist or gastroenterologist.

What do you need to know about the study?

On modern stage Anyone undergoing an occult blood test should have at least general information on this occasion.

1. The fresher the sample, the more accurate the results will be.
2. Before taking samples, simple preparation is required for several days.

The daily amount of dense excrement is approximately 200 grams. Significantly more comes out with pathological processes gastrointestinal tract, less - with malnutrition, consumption of protein foods, problems with bowel movements.

By the form you can understand whether there are deviations in the functioning of the intestines. In a healthy person, stool has a sausage shape of medium density, Brown. If abnormal, excrement can be very dense or liquid, lumps or in the form of a ribbon. In severe pathologies, not only the appearance changes, but also the composition, smell, and various impurities appear.

Normal feces may contain particles of undigested food - the norm is the peel of fruits or vegetables, cartilage or tendons.

If mucus or blood is visible to the naked eye, this indicates a disease of the colon.

How to properly collect material and test feces for occult blood?

Almost all patients know how medical staff should behave. However, few people remember that there is also a general recommendations regarding any analysis, including stool. They are as follows.

Feces are collected after natural bowel movements. The use of enemas or laxatives is prohibited. It is not recommended to use it several hours before sample collection, and special preparations for another 3-4 days. If you violate this rule, the analysis will not be accurate. However, this only applies when feces are tested for occult blood.

The accuracy of the results depends on the freshness of the material. The ideal option is if the sample reaches the laboratory within 3-6.5 hours after its collection. This rule is not always easy to follow, however, some microorganisms live outside for only a few hours. Therefore, it becomes increasingly difficult to obtain a complete picture over time. It is advisable to take the test before 10 o'clock.

3-4 days before submitting samples you need special training- dieting. You should not eat a lot of foods that cause discomfort in the stomach and intestines. Avoid foods that stain excrement, such as beets, greens, and some fruits.

If possible, do not take one week before sample collection. pharmaceutical drugs. The exception is those that are taken regularly for chronic diseases. This is due to the fact that some medications color the stool a different color or change the composition of the microflora. In addition, do not spend additional research intestines using special enemas, for example with barium. It discolors feces and changes their structure.

Collect the sample in a special jar-container with a spoon, it must be purchased in advance. To make an accurate analysis, a few grams of material is enough. It looks like about a teaspoon.

Final Rule concerns women. It is not recommended to take material during menstruation, as blood can get into the excrement and spoil the results.

Diet before stool occult blood test

A few days before the samples are taken, a special diet is prescribed, which must be followed in order for the analysis to be correct the first time.

During this period you should not eat, we repeat once again:

1. Liver in any form;
2. Legumes;
3. Fish and meat dishes;
4. Apples and other fruits that affect the color of feces;
5. Greens, particularly spinach;
6. Some vegetables: tomatoes, sweet peppers, beets, hot horseradish.

Sample menu for one day:

1. Bread and butter, milk soup, some pears or peaches, canned in winter;
2. Mashed potatoes, 2 boiled eggs, milk jelly;
3. Yogurt without dye;
4. A glass of kefir or fruit.

The amount of food taken at one time should not exceed 300-400 grams. The same set of foods with some corrections and variations should be eaten for another 2 days.

Feces for occult blood: interpretation of results

The finished analysis is called a coprogram. First of all, feces are not characterized by the presence of blood, even in the form of individual cells. Therefore, microscopic examination is done to find out whether red blood cells are present in the excrement?

They can be there for several reasons: damage to the stomach and small intestine or the lower part, that is, the rectum, colon and anus. If the bleeding is severe, the discharge is already noticeable - the feces will be black; in the case of minor damage, it is difficult to determine anything without special studies.

Damage to the bottom digestive system noticeable due to the presence of bright red impurities. Since some foods and medications can have a similar effect, you need to undergo diagnostics, that is, donate feces.

This analysis will indicate whether there are problems at the top of the food system if red blood cells are present in the material provided for the study. There are no special standards for this; even the smallest amount of blood particles in the feces is enough.

If the gums or nasal mucosa bleed, the test will be positive. Therefore, careful preparation for the procedure is necessary, and it is not recommended to brush your teeth the day before and try to avoid various injuries.