Feces for occult blood which. Fecal occult blood test - how the research is carried out

But occult blood can indicate no less formidable diagnoses, and when the disease is still at an early stage of development, and the chances of a successful recovery are much greater. That is why, if you have the first suspicious symptoms, it is necessary to obtain qualified medical advice and undergo all necessary tests. And people over 50 years of age with a history of cases colorectal cancer, you need to undergo a stool examination annually occult blood, since this simple measure can save lives in some cases.

Many pathologies of the gastrointestinal tract, including ulcerative colitis and malignant intestinal tumors, for the time being do not bother the patient with severe discomfort. But the destruction of healthy tissue is already occurring, therefore, blood is released, which cannot yet be detected visually in the stool, but this can be done with the help of special laboratory tests. Today we will tell you what a stool occult blood test shows, how to prepare for the test and what diet you need to follow, how to correctly collect and submit the material, what a positive and negative result indicates, in which cases it may be false, and what methods of determination occult blood in stool are most accurate.

Hidden blood in stool - what does it mean?

A certain amount of blood may normally be present in feces - no more than 2 mg of hemoglobin per 1 g of feces; at such a maximum concentration, it turns out that a healthy person loses up to 2 ml of blood in feces per day. If the bleeding becomes more intense, the color of the stool changes, and its shade indicates the location of the problem: the darker, the higher. For example, with a bleeding ulcer of the stomach or duodenum, the feces become black, tarry (melena), if the cause lies in an aggravated ulcer, the stool will become burgundy in color, and bleeding polyps, hemorrhoids and malignant neoplasms in the rectum lead to the appearance of scarlet streaks and spots on the feces. Such signs cannot go unnoticed and should be a reason to immediately seek medical help.

Hidden blood in stool is blood that cannot be detected either by visual or microscopic examination of stool. Only a stool test for occult blood can find it - positive result indicates the presence of hidden gastrointestinal bleeding and requires mandatory further examination of the patient.

Who is a stool occult blood test indicated for?

This type of research is prescribed in the following cases:

Persistent periodic pain in any part of the abdomen, as well as in the right or left hypochondrium;

Discomfort and pain during or after defecation;

Sensation of the presence of a foreign body in the rectum;

Loss of appetite, sudden loss of body weight for no apparent reason;

Nausea, vomiting, belching, heartburn, unpleasant taste in the mouth;

Diagnosed gastrointestinal pathologies: Crohn's disease, intestinal polyposis, diverticulosis, esophageal varicose veins, helminthiasis, and so on - the study is performed to determine the stage of the disease or monitor the progress of treatment;

Alarming results from other previously conducted examinations, for example, general or biochemical analysis blood;

Prevention of intestinal cancer over the age of 40-50 years in patients with unfavorable heredity.

Preparation, diet, collection and analysis

It makes sense to conduct a test for occult blood in feces only if the rules of preliminary preparation are carefully followed, otherwise the likelihood of obtaining a false result will be very high.

Let's start in order:

Temporarily defer analysis necessary until the following circumstances are eliminated - periodontal disease, nose bleed, menstruation, hematuria, exacerbation of hemorrhoids, recent diagnostic manipulation of the intestines (colonoscopy, sigmoidoscopy), anal sex. All these factors are likely to lead to distortion of the research results, which means that it is necessary to solve the existing problem or wait a few days, depending on the situation;

One week before the test You should stop taking any medications that have an undesirable effect on the composition of feces, namely NSAIDs (aspirin, ibuprofen, naproxen), barbiturates, anticoagulants, stimulants of intestinal motility, ascorbic acid, drugs and dietary supplements containing iron. If you are constantly taking any medications and are not sure that they will not affect the results of the study, it is better to consult your doctor in advance;

Three days before the test you need to start following a diet - fecal occult blood testing is almost always carried out using laboratory tests that are sensitive to the composition of the food consumed by the patient. Therefore, you will have to temporarily give up any meat, poultry, fish and offal - that is, everything that may not contain your blood. In addition, it is recommended to exclude from the menu some beans, vegetables, fruits and berries that are rich in iron and vitamin C or have a strong effect on intestinal motility - for example, apples, celery, cranberries, oranges, spinach, nuts, cabbage, tomatoes, carrots, beets, beans, soybeans and lentils;

12 hours before analysis needs to be postponed toothbrush and avoid eating hard foods that can injure the gums and lead to blood from the mouth entering the digestive tract.

Successful occult blood test = preparation + diet, remember this!

So, preparatory stage behind, it’s time to collect material for research and take it to the laboratory:

Early in the morning, before breakfast, perform an external toilet of the intimate area using regular soap, rinse thoroughly and dry off;

Perform a bowel movement in a previously prepared clean container. The process should occur naturally, without the use of enemas or laxatives. You cannot take a stool sample from the toilet. A fecal test for occult blood in a child is taken from a well-washed potty, from a diaper or oilcloth;

For collecting and transporting biomaterial, special sterile containers with a lid and spoon, which are sold in any pharmacy, are best suited. In the absence of such, you can use a small glass jar, having previously disinfected it. Collect a little feces from different parts of the stool so that the picture of the study is as objective as possible. A total amount of approximately 2-3 teaspoons is sufficient;

It is better to immediately deliver the container with the sample to the laboratory. However, it is permissible to store the material in the refrigerator for no more than 12 hours. This is especially useful for young children whose bowel movements are unpredictable, or people who are used to having a bowel movement before bed.

Research methods: pros and cons

Currently, four main methods are used to determine occult blood in feces:

Gregersen reaction (benzidine test);

Weber reaction (guaiac test);

Let's understand the essence of these methods, their advantages and disadvantages. Looking ahead, we note that in Russia the benzidine test and immunochemical analysis are most often used, but are they the most accurate?

Gregersen reaction (benzidine test)

The benzidine test is a simple and quick laboratory test that detects blood not only in the stool, but also, for example, in the patient’s urine, vomit and any other biological fluid. This is possible due to the oxidation of benzidine (paradiaminodiphenyl) with hydrogen or barium peroxide in the presence of hemoglobin. The benzidine test has several variations, the most commonly used of which was proposed by the doctor M. Gregersen, which is why it bears his name.

The essence of the method is as follows: take 0.025 g of benzidine, add 0.1 g of barium peroxide and 5 ml of a 50% acetic acid solution to it, shake everything until completely dissolved, apply a few drops of the composition to a glass slide, on which the feces being tested are spread in a thin layer, and watch the reaction. If there is occult blood, a bright blue-green color appears. There is an alternative option - prepare a saturated solution of benzidine in acetic acid and mix it with a 3% solution of hydrogen peroxide in equal parts. The result will look approximately the same, and the cost of the study will change little.

Pros:

Very high sensitivity – 1:100,000;

The speed of obtaining results is almost instantaneous;

Availability in any laboratory;

Low price.

Minuses:

The need for careful preparation for taking a stool occult blood test using the Gregersen method, since the benzidine test gives a positive reaction to animal hemoglobin from food.

Weber reaction (guaiac test)

In addition to the two mentioned, this diagnostic method has several more names: Van Deen or Almen-Van Deen test, hemoccult test. Interestingly, the reaction using guaiac resin is the first method in world medical practice for detecting hidden blood in human feces and other biological fluids. Dr. Van Deen proposed it in 1864 and it is still actively used in many countries.

The essence of the guaiac test is as follows: take 3-5 g of the feces being tested, dissolve it in acetic acid, which releases an ethereal extract, add hydrogen peroxide and tincture of guaiac resin to it, and then observe the color change of the reagents in a test tube. If the composition turns blue, it means that the test result for occult blood in the stool is positive. The test is repeated a total of six times: two samples from biomaterials, taken sequentially over three days, are studied.

Pros:

Efficiency.

Affordable price.

Minuses:

Low sensitivity - the reaction will be positive only in case of blood loss of 30 ml or more, colorectal cancer is detected in a third of cases, benign tumors intestines - only in 15% of cases;

Strict dietary requirements before fecal occult blood testing - the guaiac test is sensitive not only to the heme peroxidase of human hemoglobin, but also to the peroxidases of other hemes contained in food.

This analysis is otherwise called an immunological or immunochromatographic test. The technique is based on the reaction that occurs when specific antibodies interact with hemoglobin in human blood. Errors are excluded because the antibodies do not react to animal hemoglobin or iron contained in some plant foods. Immunochemical analysis of feces for occult blood appeared in the arsenal of doctors relatively recently and is already firmly established there.

The essence of the technique is as follows: a sample of the feces being tested is applied to a test strip or placed in the window of a tablet with reagents - monoclonal antibodies. If human hemoglobin is present in the biomaterial, it binds to antibodies, and a band of bright pink or purple. The second band appears in any case - it is an indicator of the good quality of the device. Taking a stool occult blood test using this method is very similar to taking a pregnancy test - everything is very simple, quick and understandable.

At the pharmacy you can purchase “ImmunoCHROM-GEM-Express” or any other similar device for self-diagnosis of hidden gastrointestinal bleeding at home, however, to obtain a reliable result, it is recommended to carry out the analysis at least three times with intervals of several days.

Pros:

Speed ​​and convenience;

No need for preliminary preparation and diet;

High accuracy - detects early stages of colorectal cancer in 97% of cases.

Minuses:

Relatively high cost;

Not available in every laboratory;

The objectivity of the results of a fecal occult blood test is only in the case of bleeding in the lower parts of the digestive tract. Aggressive enzymes acting on hemoglobin in the stomach and small intestine render it in a state unsuitable for reacting with monoclonal antibodies.

To complete the picture, it should be mentioned that occult blood can be detected in feces during a chemical reaction using destructive reagents. Nitrogen-containing pigments, porphyrins, contained in hemoglobin molecules and released when they die, have an ultra-high light absorption coefficient - about 10 to the 6th power. Their bright fluorescent glow is recorded by a laboratory technician if there is hidden blood in the stool sample being examined. However, in Russia this diagnostic method is not very popular, especially in comparison with the benzidine test.

Pros:

Efficiency;

Affordable price;

Relatively high accuracy - about 80%.

Minuses:

The need to follow a diet, since porphyrins are present in any hemoglobin, including in animals.

Decoding the results of the occult blood test

Depending on how the test was carried out and what the internal regulations of the laboratory are, you will receive an answer in 1-6 days. From the description of the methods for conducting this study, it is clear that its results cannot be expressed in an exact digital equivalent: in a benzidine and guaiac test, the reagent is either colored or not - only the speed and intensity of the coloring differs. As for the enzyme immunoassay and fluorescent tests, everything is clear here too: the second strip either appears or not, and the glow is either present or not.

As an example, let’s look at the decoding of the results of a fecal occult blood test using the Gregersen method (benzidine test):

Important: even a weak reaction usually alerts the doctor and prompts him to repeat the test or add to it additional methods diagnostics, since the presence of hidden blood in the stool is a sign of serious trouble.

Let us now consider why the results of the study may be biased:

False negative stool occult blood test result- this is almost always a consequence of a violation of the sample technology or poor quality of the reagents. It may also be that the patient provided little biomaterial or was too lazy to collect it from various fragments of feces. In addition, with some diseases of the gastrointestinal tract, for example, with colon polyposis, neoplasms do not bleed constantly, but occasionally. Therefore, it is recommended to repeat the study several times, especially if there are serious reasons to suspect the disease;

False positive occult blood test result– this, in most cases, is a consequence of neglecting the rules of preparation. Either the patient did not follow the diet prescribed by the doctor, or took any medications that distorted the picture of the study, or suffered an injury that led to blood entering the gastrointestinal tract. In infants, a positive result of a fecal occult blood test may be false if the nursing mother's nipples are cracked and bleeding - then the baby swallows blood during feeding, and it ends up in his feces. Moreover, this problem cannot be solved by pumping; in this case, blood can get into breast milk. It is better to switch the baby to an artificial formula for three days in order to have confidence in the objectivity of the test.

Positive result - what to do?

Anxious patients are primarily concerned with the question: what does a positive stool occult blood test result mean? Firstly, this is definitely not a reason to panic. We have already discussed the rather high probability of errors, especially if the rules of preliminary preparation are violated. It is imperative to repeat the study at least three times before drawing final conclusions.

Secondly, even if the positive result was reliable, it most likely signals the most common diagnoses:

[02-001 ] Fecal occult blood test

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Fecal occult blood test is a stool test performed to detect hidden bleeding from various parts of the gastrointestinal tract. It allows you to detect altered hemoglobin even in cases where the red blood cells themselves are not detected during microscopic examination of stool.

Synonyms Russian

Examination of feces for occult blood.

SynonymsEnglish

Occult blood test, fecal occult blood test.

Research method

Gregersen's test (benzidine test).

What biomaterial can be used for research?

How to properly prepare for research?

• Eliminate meat, fish, green vegetables, and tomatoes from the diet for 72 hours before the test.
• Avoid taking laxatives, administering rectal suppositories, oils, limit taking medications that affect intestinal motility (belladonna, pilocarpine, etc.) and the color of stool (iron, bismuth, barium sulfate) for 72 hours before stool collection.
• The study should be carried out before performing sigmoidoscopy and other diagnostic procedures in the intestines and stomach.

General information about the study

Analysis of feces for occult blood is an extremely important laboratory test in the diagnosis of hidden bleeding from various parts of the gastrointestinal tract. Such bleeding is one of the early symptoms of a number of serious gastrointestinal diseases, including cancer. With hidden bleeding, even long-term, it is very difficult to determine the presence of blood in the stool, both visually and microscopically, and most often simply impossible.

With heavy bleeding from various parts of the gastrointestinal tract, the blood changes so much appearance stool that its presence can often be determined visually. If the bleeding is from the lower intestines (colon, rectum), the blood will be scarlet in color, possibly in the form of clots or impurities. If the source of bleeding is in the upper gastrointestinal tract (part small intestine, esophagus, stomach), then the feces turn into black, “tarry” due to the interaction of blood and special enzymes produced in these parts of the gastrointestinal tract. As a rule, if there are visual signs of gastrointestinal bleeding, then the situation is acute and requires emergency measures ( emergency care). However, with less pronounced violations of the integrity of the gastrointestinal mucosa, with the involvement of a small number of vessels in the process, the color and consistency of the stool do not change, but red blood cells in the stool will be visible during microscopic examination. If red blood cells are not visible microscopically, but there is a suspicion of hidden bleeding, then a stool test for occult blood is required. This study carried out by measuring the amount of changed hemoglobin (and not the red blood cells themselves).

A positive stool reaction to occult blood means that a person has diseases of the gastrointestinal tract that cause disruption of the integrity of the mucous membrane when a small amount of blood is released into the lumen of the stomach or intestines. This can occur with stomach or duodenal ulcers, nonspecific ulcers, Crohn's disease, polyps, and helminth infestations. Since tumors, primary and metastatic, cause damage to the gastrointestinal mucosa even if they are small in size, the study is used at the first stage of identifying gastrointestinal tumors. The determination of occult blood is especially important when diagnosing colon cancer, since it is with tumors in this part of the intestine that occult bleeding begins in the earliest stages.

Blood in the stool can also be detected during nosebleeds, bleeding from the gums and pharynx, in patients with varicose veins of the esophagus, erosive esophagitis, hemorrhoids and other diseases, so this must be taken into account when assessing the results of the analysis.

The reliability of the analysis is highest when it is repeated. Negative test results do not exclude the possible presence of an erosive-ulcerative or tumor lesion of the gastrointestinal tract in the patient. It is important that the results should be assessed in conjunction with other instrumental and laboratory research, since they themselves cannot be the only criterion for making a diagnosis.

Sometimes all stool tests for occult blood are mistakenly called the Gregersen test or Gregersen test, erroneously because the Gregersen test (benzidine test) is the most common, but not the only method for detecting occult blood in feces, urine, vomit, etc.

What is the research used for?

• For the diagnosis of gastrointestinal diseases accompanied by violations of the integrity of the mucous membrane (peptic ulcer of the stomach and duodenum, primary and metastatic tumors of the esophagus, stomach, large and small intestines, duodenal papilla, intestinal tuberculosis, ulcerative colitis, helminthiases).
• To assess the degree of damage to the gastrointestinal mucosa.
• To assess the adequacy of therapy peptic ulcer stomach, UC, Crohn's disease, intestinal tuberculosis.
• To assess the severity of gastrointestinal disease and give its prognosis.

When is the study scheduled?

• For abdominal pain, heartburn,...
• With frequent pasty stools, false urge to defecate, weight loss, loss of appetite, increased body temperature.
• In case of identified tumors of the gastrointestinal tract (instrumental methods) to exclude hidden bleeding of the gastrointestinal tract.
• If helminths are detected, to assess damage to the gastrointestinal mucosa.
• If the patient has previously been diagnosed with a stomach ulcer (ulcerative colitis, Crohn's disease, polyposis, intestinal tuberculosis).

What do the results mean?

Reference values: negative.

Reasons for the positive result:

• colorectal cancer,
• primary and metastatic tumors of the esophagus, stomach, intestines, duodenal papilla,
• peptic ulcer of the stomach and duodenum,
• nonspecific ulcerative colitis,
• intestinal tuberculosis,
• helminthiases that injure the intestinal wall,
• dilatation of the veins of the esophagus with cirrhosis of the liver and thrombophlebitis of the splenic vein,
• Rendu-Osler disease,
• erosive esophagitis,
• nosebleeds,
• stomatitis, periodontal disease,
• haemorrhoids.

Negative result not diagnostically significant.

Stool examination provides information about the patient's health. This method helps to identify various diseases and disorders in the body.

If the patient is prescribed a stool donation, a few days before the procedure you should go on a diet - this will allow you to get reliable results from the analysis.

Nutrition in preparation for diagnosis

In this case, it is necessary to stop consuming apples, white beans, cucumbers, spinach, cauliflower, horseradish, meat and fish products. Tomatoes are also prohibited bell pepper and green vegetables.

Alcohol, sweet carbonated water, coffee, and black tea are prohibited from drinks. Pure still water is allowed.

Patients are allowed to consume potatoes, cereals, and dairy products. You need to eat in small portions without overeating. It is important to avoid frying; instead, food is boiled, stewed or baked.

Basic principles

Basic principles of the methodology:

Dishes are prepared by boiling, stewing, baking or steaming. Frying is strictly prohibited: such food can negatively affect the analysis results. The daily calorie content should not exceed 2200 kcal, the weight of the dishes should be 2.2-2.5 kg.

You need to eat food every two hours, but in small portions. There are 5-6 meals per day. The program lasts from 3 to 5 days - this is enough to prepare the body for the test.

Its effect on the body

The technique is aimed at preparing the body for the test. He is cleared of harmful substances, components that may negatively affect the result of the procedure are removed.

The person's condition will improve significantly. Excluding difficult-to-digest, high-calorie foods from the menu can lead to a decrease in body fat, and a person will lose a little weight.

Pros and cons of the method

Benefits include:

• High efficiency.
• Beneficial effect on the digestive organs.
• No need to starve.
• Help in obtaining reliable analysis results.

However, each diet has not only pros, but also cons: the patient is allowed to consume very few foods. They can get boring after a few days.

Most familiar dishes are excluded from the menu. The diet is not easy for all patients, but it is effective, so such restrictions are understandable.

There are no contraindications for this technique, but if there are chronic diseases The doctor can adjust the diet, add or exclude certain foods. It is necessary to consult a doctor.

Sample menu

In order not to make mistakes in nutrition, you need to familiarize yourself with the menu compiled by experts:

Usually the diet is followed for three days. For breakfast it is better to eat porridge or low-fat cottage cheese. For lunch, mashed potatoes, non-green vegetable stew, or boiled rice are suitable.

For dinner, fruit salads, low-fat yogurt or cottage cheese are acceptable.

When creating a menu, you should remember the lists of prohibited and permitted products.

The permitted products are very few in number and are included in the diet. The focus is on low-fat dairy products, cereals and non-green vegetables.

List of approved products

During the diet you can consume:

• Dairy products - milk, kefir, low-fat cottage cheese.
• Porridge - rice, buckwheat.
• Vegetables - potatoes, beets, carrots.
• Fruits - peaches, persimmons.
• Drinks - jelly, compote, berry juice.

It is allowed to add a little butter to dishes. During lunch or dinner, you can eat a slice of bread. The main thing is not to eat buns and flour products, they are prohibited. You can add a little sugar to tea, but you should not eat the sweets themselves..

Compotes made from dried fruits have a beneficial effect on the patient's condition. They are consumed throughout the day. This is a great addition to lunch or dinner or snack.

What not to eat

Patients should avoid the following:

• Vegetables and fruits are green.
• Meat and fish.
• Seafood.
• Nuts.
• Legumes.
• Dairy products - fermented baked milk, sour cream, yogurt.
• Drinks - alcohol, sweet carbonated drinks, coffee.

It is necessary to give up not only the food mentioned above, but also spices, flavorings, and sweeteners. Smoked meats, semi-finished products, and salted foods are also prohibited.

For the results to be reliable, you need to give up cereals such as barley, millet, wheat. They may negatively affect the diagnosis.

During the diet, experts advise strictly adhering to the menu and not consuming prohibited foods. You can't go hungry or overeat. You need to eat every two to three hours, avoiding a feeling of heaviness in the stomach.

If the patient does not have kidney problems, you should drink 1.5 liters of water per day. This will help prepare the body for the procedure.

If a person takes any medications, they are abandoned during the diet. They may affect the result of the analysis.

Intense sports training is also not recommended; walking in the fresh air is acceptable.

The technique is often used due to high efficiency. Its main principles include:

• During the day, a person consumes mainly dairy products, and fruits and vegetables in small quantities.
• It is allowed to consume cottage cheese, milk, kefir.
• Porridge is cooked with milk, and casseroles are made from cottage cheese.
• Adding sugar and sweet syrups to dairy products is prohibited.

The program lasts 3-5 days, the doctor can tell you exactly how long this diet will last. In addition to milk, you are allowed to drink water, compotes, jelly and berry decoctions.

You can add fruit to milk porridge and cottage cheese, but not green fruit. Peaches, pears, and persimmons are optimal. This diversifies the diet, making the diet easier for a person to tolerate.

Before donating stool for occult blood, a diet is necessary: ​​it helps prepare for the test, cleanses the body, and has a beneficial effect on the human condition.

Knowing the principles of such nutrition, a person will do an excellent job of preparing the body for analysis, and the results will be reliable.

In contact with

Examination of stool for the presence of occult blood is an important component of diagnosis. various diseases Gastrointestinal tract (gastrointestinal tract). With its help it is possible to recognize oncological diseases in the early stages, accompanied by bleeding to varying degrees, which allows treatment to begin on time and save the lives of many patients.

Having discovered blood in their feces, most people will rush to the hospital, because they understand that such a signal is serious and requires immediate medical attention. But dangerous diseases do not always have such pronounced symptoms. Therefore, if there is a suspicion of organ pathology digestive system A stool occult blood test is often prescribed, which makes it possible to detect even minor bleeding.

Why is occult blood dangerous?

Blood impurities, invisible to the naked eye, can be no less dangerous than clearly diagnosed bleeding. One such disease is colorectal cancer, a malignant neoplasm that affects the colon and rectum.

In the early stages, bleeding from the resulting tumor may be insignificant, so it is difficult to detect it without testing. In addition, the rest of the symptoms at the onset of the disease are also not clearly expressed, which significantly complicates the diagnosis.

Attention! For people over 45–50 years of age who have a family history of colorectal cancer, annual stool occult blood testing is recommended to increase the chances of detecting the disease in its early stages.

Gastrointestinal pathologies such as ulcerative colitis, polyposis, diverticulosis, etc. are no less dangerous. They may also not bother the patient for a long time with noticeably pronounced manifestations, and he will think that temporary ailments are associated with banal reasons, for example, with poor nutrition.

But at this time, healthy tissues are gradually destroyed, and minor impurities of hemoglobin or modified red blood cells enter the feces, which cannot be detected without special devices.

What does occult blood mean?

Normally healthy person a small amount of blood may be present in the stool, but not more than 2 mg of hemoglobin per 1 g of feces. At this concentration, it turns out that about 2 ml of blood is released from the body per day, and this does not cause any harm.

In the case when the bleeding intensifies, the color of the stool changes, and its shade can indicate the localization of the pathology, that is, the darker it is, the higher the problem is located in the gastrointestinal tract. For example, with a bleeding stomach or duodenal ulcer, the feces become black and tarry (melena).

If the cause is hidden in an exacerbation of ulcerative enterocolitis, then the feces will be burgundy. With bleeding hemorrhoids, polyps and malignant tumors of the rectum, streaks and drops of blood will be present in the stool. Such symptoms should in no case be ignored, and the sick person should visit a specialist as soon as possible and undergo all the necessary tests.

Hidden blood in feces is hemoglobin or red blood cells, which are not detected either by visual or microscopic examination of stool. It is shown only by the described analysis, and a positive result confirms the suspicion of hidden bleeding of the gastrointestinal tract, which requires immediate further examination and the appointment of appropriate therapy.

Intestinal damage due to a colorectal tumor may be accompanied by the appearance of occult blood in a stool test

When is diagnostics required?

Testing for occult blood in feces is prescribed to a fairly wide range of patients, since gastrointestinal pathologies are very common not only in our country. Therefore, a referral for examination will be issued for the following symptoms:

In addition to alarming symptoms, there are several other circumstances that cause a single or repeated analysis. These include:

• Diagnosed gastrointestinal diseases: intestinal polyposis, esophageal varicose veins, diverticulosis, Crohn's disease, ulcerative colitis (UC), helminthiasis and quite a few more big list. The procedure can be used both to determine the stage of pathology and to monitor ongoing therapy.
• Alarming results of previously conducted other diagnostics, for example, a clinical blood test or biochemical test, coprogram, etc.
• Prevention of the development of cancerous tumors in the intestines in people over 40–50 years of age and in patients with a family history.

Preparing for the examination

This procedure, as well as clinical analysis stool, as well as many other techniques, requires preliminary preparation. Moreover, the requirements are several times greater compared to some tests, but they cannot be neglected, since otherwise the result will not be reliable, and the biomaterial will have to be taken again.

Firstly, you should delay collecting biomaterial until stomatitis, periodontal disease, dyspepsia, hematuria, nosebleeds, and exacerbation of hemorrhoids are eliminated (if any). Preparation also means waiting 3–4 days after the diagnostic procedures in the intestines (sigmoidoscopy, colonoscopy), anal sex, and for women - the end of menstruation. All of these circumstances are highly likely to distort the results of the study.

Secondly, a week before the test, you should temporarily stop taking medications that can change the composition of stool. Specifically, NSAIDs (aspirin, naproxen, ibuprofen), anticoagulants, ascorbic acid, barbiturates, agents that stimulate peristalsis, iron-containing medications and dietary supplements.

Important! If the patient takes any medications on an ongoing basis and does not know whether their use can affect the test results, then it is imperative to consult with your doctor in advance.

Thirdly, 3-4 days before the examination you need to start following a special diet. The fact is that diagnosis of occult blood is almost always performed using samples that are highly sensitive to certain food components. That is why before analysis you need to give up all types of meat, fish, poultry and offal. This will allow laboratory diagnostic specialists to detect only the blood of the person being examined.

In addition, you should refrain from eating a certain list of fruits, berries, vegetables and legumes that contain a lot of iron or vitamin C. You should also not eat foods that increase intestinal muscle motility - cabbage, apples, carrots, tomatoes, celery, beets, oranges, nuts, spinach, cranberries, soy, lentils and beans.

Rules for preparing for the examination

Fourth, 12 hours before the procedure, stop brushing your teeth and eating hard foods, which can injure the gums and thereby cause blood to enter the gastrointestinal tract. It is very important not to forget to follow all the rules and prepare properly for the examination, then you can say with confidence that the result obtained can be trusted.

Algorithm for collecting and donating feces

After all preparatory requirements have been met, you can proceed to collecting biomaterial. Before defecation, it is necessary to carry out hygiene procedures for the genital area and anus using soap. When finished, rinse these organs well and wipe dry.

You should empty your bowels into a special clean container, which is prepared in advance. To obtain a sample, bowel movements must occur naturally, without the aid of laxatives or enemas. You cannot collect biomaterial from the toilet, and in children, feces are taken from a thoroughly washed potty or oilcloth or diaper (not from diapers).

Reference! It is best to collect and transport the sample in specially designed sterile containers, equipped with a spoon for convenience and having an airtight lid. They can be purchased inexpensively at any pharmacy.

If it is not possible to purchase a container, then you can use any glass container with a lid, which must be thoroughly washed and sterilized. A sample is taken from several areas of feces so that the diagnostic picture is as informative as possible. In total, you need to collect 2-3 teaspoons of biomaterial.

If possible, it is best to take the container with the sample to the laboratory immediately after collection, but it can also be stored in the refrigerator for up to 12 hours. The latter action allows you to not be tied to a clearly specified time, which is convenient when examining small children whose stool is unpredictable, as well as patients who have bowel movements before going to bed at night.

Research methods

Modern medicine has in its arsenal several methods of analysis indicating the presence of occult blood, but the following 4 are often used:

• benzidine test (Gregersen reaction);
• guaiac test (Weber reaction);
• immunochemical analysis;
• fluorescence test.

At the same time, in Russia the most common research methods have become the Gregersen reaction and immunochemical analysis.

Benzidine test

A fairly quick and simple test that detects hidden blood not only in excrement, but also in vomit, urine and other biological fluids. This can be done using the oxidation reaction of benzidine (paradiaminodiphenyl) or barium with hydrogen peroxide in the presence of hemoglobin. This technique has several options, and the most preferred one is named after its creator, doctor M. Gregersen.

The essence of the test: 0.025 g of benzidine is combined with 0.1 g of barium peroxide and 5 ml of 50% acetic acid, mixed until completely dissolved and applied to a special glass covered with a thin layer of excrement. If blood is present, a reaction occurs accompanied by a blue-green color. There is also another option - prepare a concentrated solution of benzidine and acetic acid, which is then combined with 3% hydrogen peroxide in equal proportions. The result and price of the analysis remain virtually unchanged.

Advantages of the method: ultra-high sensitivity - 1:100,000, instant results, low cost and availability in almost all laboratories. Disadvantages: the need for scrupulous preparation before taking the test, since the test will be positive if there is animal hemoglobin in the food.

A device for detecting hidden blood in excrement for home use

Weber's reaction

Diagnostics is also called hemoccult test and Almen-Van Deen, or Van Deen test. The reaction using guaiac resin became the first method in world practice for the determination of blood in biological fluids of the body. It was developed by Dr. Van Deen back in 1964 and has been successfully used in most countries to this day.

The essence of the method: 3–5 g of biomaterial is placed in acetic acid, followed by isolation of an ethereal extract, to which a tincture of guaiac resin and hydrogen peroxide is added. If the resulting composition turns blue, it means that the test result is positive. The procedure is repeated 6 times, and during it, 2 stool samples taken on three consecutive days are studied.

The advantages of the method: speed and low cost. Cons: relatively low sensitivity– a positive result will be only with blood loss of more than 30 ml, which makes it possible to detect colorectal cancer in one third of cases, and benign neoplasms in no more than 15%. The technique has strict requirements for dietary restrictions. She is sensitive to all types of hemoglobin, so a diet is required.

Immunochemical analysis

This diagnosis is also called an immunochromatographic or immunological test and is new, but has already firmly strengthened its position. It is based on the interaction of human hemoglobin with specific antibodies (AB). Inaccuracies and errors in this analysis are excluded, since ATs do not react to other types of hemoglobin or iron included in the products.

The essence of the method: a sample of the taken biomaterial is applied to a test strip or into the window of a tablet equipped with reagents. If it contains human hemoglobin, then binding to AT occurs, resulting in a purple or bright pink stripe in the control zone. In this case, the second strip is necessarily present - it is an indicator of the quality of the device. This diagnostic method is very similar to a pregnancy test and is also commercially available. It is very fast, simple and extremely clear.

Pros: speed and comfort, no need to diet and produce preliminary preparation. The test is highly accurate. It is able to show colorectal cancer on initial stages in 97% of cases.

Disadvantages: quite high price, it is not available in every laboratory even in Moscow, it is only effective for bleeding in the lower parts of the gastrointestinal tract. Since the enzymes of the stomach and small intestine aggressively affect hemoglobin, and it loses the ability to bind to AT.

Fluorescence test

Occult blood can be detected in excrement by reaction using destructive reagents. Porphyrins are released when the molecular structure of hemoglobin is destroyed. They have a high light absorption coefficient - approximately 10 6, and in the presence of blood a bright fluorescent glow is recorded.

It should be noted that this method is not popular in Russia. Pros: low cost, speed, relatively high accuracy - approximately 80%. Cons: you need to follow a diet, since porphyrins are included in the molecule of any hemoglobin.

Interpretation of study data

It is difficult to answer the question of how much analysis is done. Everything will depend on the methodology and workload of the laboratory, so the process can take from 1 to 6 days. In itself, deciphering the fecal occult blood test is quite easy - specific digital indicators are not used to determine the norm, but only the intensity and speed of staining (in the benzidine and guaiac test) are studied.

Regarding the fluorescent and immunochemical tests, everything is just as simple - there is a glow or not, a second strip appears or not. The first two methods are evaluated according to the following principle. Minus – no reaction, plus – weakly positive result, 2 pluses – moderately positive result, 3 pluses – strongly positive and 4 pluses – super intense result.

Attention! Even a weak result should alert the doctor and cause a repeat test or additional examinations, since hidden blood is a very dangerous symptom.

Recommendations for patients. Analysis of excrement for occult blood is a simple and inexpensive diagnosis, which makes it possible to identify dangerous gastrointestinal diseases. Therefore, you should not refuse it if the doctor recommends, but despite minor difficulties in preparation and, possibly, the unpleasant process of collecting the sample, undergo the procedure. This examination helped save many patients from dangerous diseases and give them a second chance at a healthy life.

Fecal occult blood testing is widely used to diagnose bleeding in gastrointestinal tract. If the preparation is incorrect or the material is collected incorrectly, false-positive reactions may occur that change the diagnostic picture. Therefore, you need to know how to properly prepare for the study.

Causes of blood in stool

The main and most common cause of occult blood in the stool is tumor processes in the intestines (colorectal cancer). Hidden blood in stool is that which is not visible visually or even under a microscope. It is known that intestinal tumors bleed. There is a small amount of this blood in the initial stages of the disease. Once in the intestinal lumen, red blood cells and along with them hemoglobin are destroyed by digestive enzymes and therefore become invisible.

In addition to colorectal cancer, the causes of the appearance of occult blood in the stool of an adult can be polyps in the intestines, any inflammatory process, ulcerative process in the intestines, diverticulosis (pockets in the intestines), Crohn's disease, ulcerative colitis (UC).

Why is research needed?

A stool occult blood test shows the presence of invisible hemoglobin and red blood cells. The study is very valuable in determining intestinal bleeding in the early stages, when it is not yet visible to the eye. In what cases is a stool test for occult blood indicated? Below are the main factors:

• Pain or discomfort during or before bowel movements.
• Any impurities in stool (mucus, foam).
• Changes in stool character. It has become liquid or, on the contrary, too dense.
• Traces of blood are periodically visible in the stool.
• Decreased appetite or significant weight loss.
• Abdominal pain of any location.
• The presence of symptoms such as heartburn, nausea, vomiting, iron taste in the mouth.
• Periodic causeless increase in body temperature.
• Annually as a screening examination for patients over 40 years of age. It is carried out for the early detection of colon tumors.

If you have any of the above symptoms, it is recommended to have your stool tested for occult blood.

Preparing for a stool occult blood test, what is it for?

Patient preparation is necessary only in case of analysis by chemical reactions (benzidine, guaiac tests). These tests often give false positive reactions, for example to animal hemoglobin found in meat foods, or to chemicals in food and vitamins.


Today there is an analysis that does not require special preparation of the patient. This is an immunochemical stool occult blood test. It is based on the interaction of antibodies only with human hemoglobin, so the analysis is more specific and sensitive than standard chemical tests.

It should be borne in mind that the analysis is reliable only for bleeding from the lower intestines (colon and rectum). In the upper sections, hemoglobin is significantly affected by digestive enzymes and is destroyed. Therefore, after the study, if the result is positive, it is recommended to undergo additional examination (colonoscopy, for example).

How to prepare for the analysis?

1. Diet before stool occult blood test. For three days (72 hours) you need to exclude food of animal origin (meat, fish) from your diet. You should also exclude some vegetables, especially green ones: cauliflower, cucumber, horseradish, green apples, spinach, lettuce, any greens and zucchini. Tomatoes are also excluded.
2. The use of iron containing products is not recommended medicines, bismuth and barium sulfate. Also, on the eve of the test, you should not take acetisalicylic acid (aspirin) and ascorbic acid (vitamin C).
3. Three days before the study, it is not recommended to carry out any diagnostic or therapeutic manipulations with the intestines (x-ray contrast study, sigmoidoscopy, colonoscopy).
4. You should not use laxatives or give enemas. Material for analysis is collected after three spontaneous bowel movements from different areas of the stool.
5. This test is not recommended for menstruating women.

How to get tested correctly?

For a reliable result, after proper preparation, you need to collect the feces in a specially designed container purchased at the pharmacy. The material should be taken after natural emptying from several areas of stool. The amount of material is sufficient in the amount of 1 teaspoon.

Decoding the analysis results

A positive test reaction indicates processes in the intestine that lead to a violation of the integrity of its mucous membrane. This means that red blood cells and hemoglobin enter the intestinal lumen. But you should not rely only on the results of one analysis. A number of diseases of the intestines and other organs can give a positive reaction. For example, nosebleeds, stomach polyps, ulcerative lesions of the esophagus, hemorrhoids and even helminths. To make an accurate diagnosis, a complete examination of the patient is necessary.

The test result may also be false positive if a reaction occurs not to human hemoglobin, but to substances or dyes contained in food. This usually happens when the patient is incorrectly or insufficiently prepared for the study. In any case, a positive result is a reason for a more in-depth examination of the patient.

A negative test result is the norm for a person. But this result does not always indicate the absence of intestinal bleeding and should not reassure either the patient or the doctor. A negative result has no diagnostic value. For greater reliability when negative result the analysis can be repeated three times.