Few people, having emptied their bowels, think that based on the characteristics of this biomaterial one can judge the presence of such serious pathologies, such as stomach ulcers, Crohn's disease, polyps and malignant neoplasms intestines.

To identify them, you will need to undergo stool tests. occult blood. Diagnosis does not take much time, is painless and allows you to suspect the development of ailments even at an early stage.

Fecal occult blood test - what is it?

In some pathologies of the rectum, for example, internal hemorrhoids or anal fissure, inclusions of scarlet blood are visible to the naked eye in the stool.

However, when bleeding occurs in the small intestine, a different picture is observed. Blood components are digested by enzymes, mixed with feces and excreted. In this case, the blood loses its scarlet color. If the bleeding in the small intestine is severe enough, the stool may turn black - this is alarm signal. However, such a clinical picture does not always develop.

More often, the components of digested blood are mixed with feces and become indistinguishable to the naked eye. You can't even look at them with a microscope. This is what is called hidden blood.

It can be detected in feces in the following ways:

• guaiac or benzidine test;
• immunological method;
• fluorescence analysis.

Chemical tests

Historically, reactions with guaiac and benzidine were the first to appear in the arsenal of diagnostic methods. The principle of their action is based on the fact that blood hemoglobin is a strong oxidizing agent. By reacting with substances such as benzidine and guaiac, it changes their color. The more hidden blood in the stool, the more intensely and quickly the color of the reagents changes.

The disadvantage of the method is the relatively low sensitivity of these samples. The reaction with benzidine allows one to detect a daily blood loss of at least 15 ml. Normally, a person can lose up to 1 ml of blood per 24 hours during bowel movements.

Slight increases in this indicator can warn of the first stages various pathologies Gastrointestinal tract, but a benzidine test cannot detect them.

The reaction with guaiac is more accurate, but it can also warn about incipient colon cancer in only 50% of patients. In the case of colorectal oncopathology, the sensitivity of the method does not exceed 30%.

Both tests can give false positive results. Most often this is due to improper preparation for the analysis.

Immunochromatography method

Immunochemical analysis of stool is more advanced. It is convenient, standardized and simple. Immunochromatographic determination of occult blood is similar to the procedure for performing a pregnancy test.

Monoclonal antibodies are used to perform this stool test. The prepared biomaterial sample is applied to the test strip.

Monoclonal particles bind to human hemoglobin, forming a colored complex compound. Further, it is captured by other antibodies localized in the control area, and two marks appear on the test strip if the concentration of occult blood is higher than normal. Otherwise, one stripe is visualized.

The immunochemical method is highly sensitive and does not require special preparation. It can detect mild bleeding in the early stages of colon cancer in 97% of cases. However, the analysis is not suitable for diagnosing diseases developing in the small intestine.

Fluorescence analysis

The breakdown products of hemoglobin in feces can also be detected using fluorescence. In this case, the biomaterial is processed in a special way, and its glow is recorded. It is known that porphyrin pigments, which are part of hemoglobin molecules, can be detected by fluorescence when the latter is destroyed.

This method is quite accurate, but if a person eats meat the day before, animal hemoglobin will appear in his stool - this will cause a false result.

IN lately Another diagnostic approach has been developed. Human DNA is extracted from the stool sampled for analysis and examined for changes characteristic of the tumor process.

When should you take a stool occult blood test?

Obviously, the study is indicated when there are signs of violations on the part of digestive system. The following symptoms should be the reason for the analysis:

• heartburn;
• stomach ache;
• change in stool character;
• nausea or vomiting that persists for a long time;
• mucus impurities in stool;
• foamy inclusions.

In addition, everyone over the age of 40 should have an occult blood test every year. This is the best measure for the timely detection of inflammatory and especially oncological pathologies. The following clinical picture can warn about the development of a malignant process in the gastrointestinal tract:

• regular increase in body temperature for no apparent reason;
• decreased appetite;
• aversion to meat food;
• sudden loss of body weight;
• constipation;
• painful sensations during bowel movements.

In addition, if visible to the naked eye appears from time to time in the stool spotting, or the stool turns black, you should not delay the analysis. These signs warn of bleeding caused by polyps, tumors, erosions or ulcers.

How to prepare for the analysis?

Taking a stool occult blood test requires special preparation. Depending on which research method or methods will be used, the patient will have to adhere to a certain regimen.

Diet

Chemical sampling and fluorescence analysis are non-selective. They identify the components of not only human, but also animal hemoglobin obtained from food. For this reason, before such a fecal occult blood test, a diet is indicated that involves a complete abstinence from meat, fish, and poultry. Any by-products are also prohibited.

In addition, when preparing for a stool occult blood test, you should not eat foods rich in iron:

• beans;
• pomegranate;
• bell pepper;
• tomatoes;
• spinach, parsley;
• apples;
• Brussels sprouts, broccoli;
• carrot.

If the study is carried out using immunochromatography, the need for a special diet disappears. Monoclonal antibodies bind exclusively to human hemoglobin and do not react to compounds of other origin.

Medicines and treatments

The diet must be followed for at least 3 days before the analysis. At this time, it is also important to completely stop taking iron supplements, ascorbic acid and all non-steroidal anti-inflammatory drugs (Aspirin, Ibuprofen, etc.).

During this period, you should refrain from any procedures that could theoretically disrupt the integrity of the intestinal and gastric mucosa. You cannot give enemas, undergo fibrogastroscopic examination, undergo irrigoscopy, sigmoidoscopy, or colonoscopy. Even laxatives are prohibited. You need to stop taking them at least a week before the test.

Since the last x-ray examination At least 3 days must pass before the stool is collected for analysis.

Other Features

Some diagnostic methods are highly sensitive and can detect even minimal amounts of blood in the biomaterial. For this reason, in order to avoid false results, on the eve of the test you should refrain from brushing your teeth, because bleeding from the gums is not uncommon.

Women should not have stool tested during menstruation. Even what happened the day before can distort the results nosebleed. In addition, when collecting material, it is important to ensure that no urine gets into it.

Features of collecting biomaterial

Feces for analysis are collected in a sterile special container. You can buy it at the pharmacy.

• Biomaterial should be collected from different parts of the feces: 2-3 fragments.

After this, it is important to place the container in the refrigerator and deliver it to the laboratory within 3 hours.

The less time passes from the moment of collection, the better.

Interpretation of stool occult blood test

Immunochemical analysis and tests with benzidine and guaiac are semi-quantitative methods for determining occult blood. The first diagnosticum answers the question: does the hemoglobin concentration in a stool sample exceed the normal value?

• If a laboratory technician or patient at home sees 2 marks on the test strip, the answer is yes. One control is negative.

When testing with guaiac and benzidine, the intensity and speed of coloring of the reagents is assessed. The reaction can be of 5 types:

• negative (no color change);
• weakly positive (+);
• positive (++);
• positive (+++);
• sharply positive (++++).

Fluorescent analysis is a quantitative method. It is not sensitive at porphyrin concentrations up to 2 mg/g of biomaterial. But when their content in 1 g of feces is equal to or exceeds 4 mg, pathology is diagnosed. The test is also able to detect borderline values: from 2 to 4 mg.

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Types of stool occult blood tests

The obvious presence of blood in feces ah – alarming symptom, indicating the presence serious illnesses. The localization of the pathological process can be indicated by the color of the blood impurity: the lighter and brighter it is, the lower the affected organ is located. If scarlet blood is visible in the stool, pathology is present in the lower intestine. Bleeding from the transverse and colon leads to the appearance of a burgundy color. Black, tarry (melena) stool appears with malignant lesions and ulcerative bleeding from the stomach and duodenum.

Important! To figure out what the changed color, smell, and consistency of the discharge mean, you need to see a doctor. You cannot start self-medication.

Not always serious illnesses accompanied by severe symptoms. To detect microscopic inclusions of blood in feces, a special biochemical analysis. To study this material for occult blood, the following analysis methods are used:

• guaiac (guaiac);
• benzidine test;
• immunochemical method;
• fluorescent.

All these methods have both positive aspects, and disadvantages.

Tests using guaiac glue and benzidine can quickly determine blood in the stool (rapid methods). Their essence is that the hemoglobin contained in a sample of material becomes colored when exposed to an oxidizing agent in blue. The use of benzidine is also called the Gregersen method. The disadvantage of the benzidine test is its reaction to foreign (non-human) hemoglobin. The advantage is speed.

Hidden blood in stool is the amount of blood at which the color of the stool remains unchanged, and blood particles cannot be determined when examined under a microscope. The norm is its absence in feces (negative result). This is a somewhat arbitrary definition, since hemoglobin is still present in very small volumes in this sample (in an amount of about 2 mg per 1 kg of discharge). 1–2 mg of blood excreted in feces per day is normal.

The table shows the explanation of the graphic designation of the reaction with the benzidine test:

*The result of the analysis is determined by the reaction rate and the color intensity of the reagent. These characteristics, in turn, are determined by the concentration of hemoglobin.

** A weakly positive result is a reason to prescribe other tests to clarify the diagnosis or retest stool for occult blood if you suspect that the material was collected incorrectly.

** It is possible to use the term “traces” instead of graphic designation.

With the guaiac test, the speed of the method and low cost are also positive points. The downside is that it has little sensitivity: guaiac acid reacts to hemoglobin in the sample if blood loss is at least 30 ml.

Important! Benzidine is not used for laboratory testing in many countries because it is a carcinogen. Guaiac and benzidine tests are the very first methods for detecting the presence of blood pigments in stool.

Immunochemical analysis is more accurate. It uses the reaction of the antibodies of the person being examined to exposure to antigens. It is also used for diagnostics infectious diseases(determination of the type of pathogens that caused inflammatory process in the digestive tract). The disadvantages include the fact that the immunochemical test takes 14 days.

Important! The immunochromatography method shows bleeding and tumor formations in the colon with high accuracy, but it is not suitable for diagnosing diseases small intestine.

Fluorescent analysis is based on detecting the glow of a material sample after processing special composition, destroying hemoglobin. Disadvantage: reacts to animal hemoglobin. But this can be avoided if you prepare properly for the test.

The doctor prescribes an occult blood test in the following cases:

• a person experiences pain in the abdominal area in the absence of other symptoms;
• for a long time the patient experiences dyspeptic symptoms (heartburn, belching, nausea and vomiting);
• the organoleptic quality of stool changes (liquid with the inclusion of foam or mucus, unpleasant smell, etc.)

To pass the tests correctly, you need to prepare for the test three days in advance. Preparation includes, first of all, changing your diet. The diet will ensure clear results, as some foods contain iron and others may stain the feces, which can skew the sample reaction. Along with the referral for analysis, the doctor must give the patient a list of what can and cannot be eaten.

You need to give up the following within 72 hours:

• spinach, apples, green fruits, meat, fish and other products with high content gland;
• tomatoes, blueberries, pomegranates, blackberries and other fruits with red pigment;
• liver and other offal;
• horseradish, radishes, cucumbers, cabbage, legumes.

Important! No diet is required for immunochromatographic studies.

A person needs to give up medications (except for those that cannot be avoided, but this must be discussed with a doctor). Ibuprofen, Aspirin, Ascorutin, iron supplements, vitamin C (ascorbic acid), laxatives are not recommended on the eve of the test. A week before the procedure, medications that affect the color of discharge and intestinal motility are discontinued.

The following should not be done before donating stool:

• X-ray examination;
• enemas and other cleansing procedures.

Teeth are not brushed the day before. The reason is that microtrauma of the gums can lead to some amount of blood entering the esophagus, which will affect the result.

The patient should defecate naturally, without the use of stimulants, and place three stool samples after one bowel movement into a plastic, tightly closed container (or use three containers for this). One sample should contain an amount equal to 1 tsp.

Important! The collected material must reach the laboratory no later than 3 hours after collection.

The sample must be clean - not contain any foreign liquid or solid substances. Therefore, it is best to go to the toilet either on a toilet covered with oilcloth, or on a chamber pot, washed with boiling water and dried. If a woman is menstruating, you need to wait until critical days will end.

Analysis transcript

Interpretation for adults and children is carried out only by a doctor who knows how to interpret tests. A specialist will figure out what the analysis obtained by one or another research method (or several) shows.

Important! Nasal bleeding (when blood enters the esophagus) and dental diseases accompanied by inflammation and bleeding of the gums.

Norm

In a healthy person, tests do not detect hemoglobin particles in the stool, although objectively about 2 ml of blood enters the gastrointestinal tract per day.

False results

Test results are defined as false positive and false negative if they do not correspond to the actual state of the gastrointestinal tract. False positive test may appear if the delivery rules are not followed (eating the wrong food, gum injury, etc.). In these cases, the sample indicates blood particles in the absence of actual pathological processes in the intestines and stomach. A false negative result occurs if the disease causes irregular bleeding. An analysis taken during the period of remission will not show traces of hemoglobin.

The meaning of positive and negative results

If the test result is negative, this means that no significant amount of blood was detected in the sample. With a positive analysis, a pathological process is present. This could be an inflammatory disease, tumor, infection, mucosal injury, hemorrhoids, cracks, helminthic infestation.

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Reasons

An occult blood test is prescribed by the attending physician in case of suspicion of bleeding in the gastrointestinal tract. This problem can become a sign of many diseases, including cancer.

Oncological problems with the large intestine are already initial stage manifestations may cause constant mild bleeding. They appear due to the fact that neoplasms consisting of cancer cells often bleed and blood directly enters the large intestine.

In this case, blood in the stool can be detected using a routine test. But in rare cases, blood can be detected only when occult blood test.

A positive test result may be caused by the following diseases:

• helminthiasis (infection with large helminths that can injure the intestinal walls);
• polyposis (proliferation of polyps in the intestines);
• ulcer (inflamed intestinal microtrauma caused by bacteria);
• inflammatory processes in the gastric mucosa and intestines;
• hemorrhoids and hemorrhagic diathesis;
• typhoid fever;
• stomach pathologies;
• Crohn's disease;
• neoplasms in the large intestine;
• pathology of the duodenum;
• cancerous tumors.

Decoding

Occult blood can only be detected by microscopic analysis or hemoglobin test ( guaiac test). Tests based on monoclonal antibodies that react to the presence of hemoglobin are allowed.

The high sensitivity of such tests allows them to be considered significantly better than conventional express methods.

It is worth considering that in some cases a completely healthy person can have a positive reaction, so only specialists can accurately determine the disorder.

Normal the reaction to occult blood must be negative.

If the reaction is positive, there is a suspicion of chronic pathologies associated with the gastrointestinal tract. Usually these are damage to the mucous membrane.

In this case, blood can penetrate into the lumen of the thick or small intestine, stomach. However, such a disorder can only be detected using an occult blood test.

Also reasons for a positive reaction may be:

• colitis;
• duodenal ulcer;
• nonspecific ulcerative colitis.

What to do if the test is positive?

If the test is positive, it is necessary to undergo diagnostics. This should initially be a colonoscopy. This diagnosis allows you to see the exact location of the lumens in the lower intestine.

If necessary, you can perform a biopsy, after which more accurate information will be obtained about the cause of occult blood in the stool.

If the cause of this pathology is the development of a tumor, in the future you will have to consult an oncologist, as well as conduct magnetic resonance imaging.

Treatment

Treatment after a positive test result is detected, should only be discussed with your doctor.

Positive test in infants and children under three years of age

Any change in the concentration and color of a baby's stool causes concern among parents. But with a single stool change there is no need to worry. But if scarlet impurity in the stool appears regularly, you need to consult a doctor and take a test for occult blood in the stool.

Enough common cause the appearance of blood in the stool is baby intolerance to cow's milk. Problems can arise even if the milk is consumed by the baby's mother, who continues to breastfeed. Problems can also begin if the mother eats butter, sour cream, cheeses and other dairy products.

If the child is bottle-fed, it is necessary to carefully select a formula that does not contain cow's milk protein.

If a baby tests positive for occult blood in the stool, the problem may be inflammatory diseases intestines:

• dysbacteriosis;
• amoebiasis;
• colitis;
• dysentery;
• balantidiasis.

An accurate diagnosis can only be established based on examination and coprogram.

Another cause of occult blood in the stool can be an infection caused by the introduction of adult foods to the baby’s food.

This problem may also be accompanied by vomiting, diarrhea, abdominal pain, and high fever.

In older children (from two years old), a positive reaction to occult blood in the stool can be observed in case of problems in the large intestine - juvenile polyps. Such formations do not cause discomfort to the child and are not dangerous to his health. If desired or necessary, they can be removed.

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Blood cells under a microscope

Normal at proper preparation the patient's occult blood is not detected in the stool. Bleeding from the gastrointestinal tract is a problem that practitioners often encounter. The degree of bleeding varies greatly, and the greatest difficulty is in diagnosing small chronic bleeding. In most cases, they are caused by cancer of the gastrointestinal tract. Colon tumors begin to bleed in the early (asymptomatic) stages of the disease, causing blood to leak into the colon.

To diagnose bleeding from the gastrointestinal tract, various screening tests are used to identify externally healthy people asymptomatic course of the disease, which allows achieving a positive treatment result.

Normally, 1 ml of blood is excreted in feces per day (or 1 mg of Hb per 1 g of feces). As it moves through the intestines, blood is distributed in the feces and undergoes breakdown under the action of enzymes (digestive and bacterial).

To detect occult blood in stool, most clinics use benzidine or guaiac tests. Hidden blood is blood that does not change the color of stool and is not detectable macroscopically or microscopically. Reactions to detect occult blood are based on the property of the blood pigment Hb to accelerate oxidative processes. An easily oxidized substance (benzidine, guaiac) changes color when oxidized. Based on the speed of staining and its intensity, weakly positive (+), positive (++ and +++) and strongly positive (++++) reactions are distinguished.

When ordering a stool test for occult blood, special preparation of the patient is necessary (to avoid false-positive results). 3 days before the study, exclude from the patient’s diet meat dishes, fruits and vegetables containing a lot of catalase and peroxidase (cucumbers, horseradish, cauliflower), cancel ascorbic acid, iron supplements, acetylsalicylic acid and other non-steroidal anti-inflammatory drugs. To detect occult blood, it is recommended to examine stool after 3 consecutive bowel movements, and each time samples are taken from two different places in the stool. When assessing the results of the analysis, even one positive result should be considered diagnostically significant (even in cases where the rules for preparing the patient were not followed).

The diagnostic value of the occult blood test in terms of early diagnosis of colon cancer depends on the amount of bleeding from the tumor. On average, blood loss from tumors of the cecum and ascending colon colon is 9.3 ml/day (from 2 to 28 ml/day) [Henderson D.M., 1997]. In localizations distal to the hepatic flexure of the intestine, blood loss is significantly less and amounts to 2 ml/day. This difference may

but, due to the large size of tumors of the proximal colon. Blood loss from an adenomatous polyp averages 1.3 ml/day, regardless of its location.

The reactions used to detect occult blood in stool vary in sensitivity. The reaction with benzidine can only detect blood loss exceeding 15 ml/day, gives many false-positive results and is currently practically not used. The most common test for detecting peroxidase activity in clinical practice is guaiac test. Typically, this test involves placing stool on filter paper and then adding guaiac, acetic acid, and hydrogen peroxide. In this setting, the method is very sensitive for detecting peroxidase activity, but is poorly standardized and often gives false-positive results. In this regard, tests were developed in which the guaiac reagent was pre-applied to a plastic strip, which made it possible to standardize the examination and diagnose even minor bleeding.

The rate of positive guaiac test results depends on the amount of blood in the stool. The test is usually negative when the concentration of Hb in feces is less than 2 mg per 1 g and becomes positive when this concentration increases. The sensitivity of the guaiac reaction at a Hb concentration of 2 mg per 1 g of feces is 20%, and at a concentration of more than 25 mg per 1 g - 90%. In approximately 50% of cases of colon cancer, the tumor “excretes” enough blood to be detected by the guaiac reaction, the sensitivity of which in colorectal cancer reaches 20-30%. The guaiac test also helps in diagnosing colon polyps, but blood loss from polyps is much less, so the test for diagnosing this pathology is not sensitive enough (positive in about 13% of cases). Polyps of the distal part of the colon (descending colon, sigmoid and rectum) give positive results in 54% of cases, proximal - in 17%.

The Hemoquant quantitative test (based on fluorescent detection of porphyrins in feces) is twice as sensitive as the guaiac reaction, but may be affected by meat intake and intake. acetylsalicylic acid within 4 days before analysis. Normally, the content of porphyrins in feces is less than 2 mg/g of feces; 2-4 mg/g - border zone; above 4 mg/g – pathology.

Considering all these shortcomings of traditional screening tests, in recent years a completely new new method diagnosis of bleeding from the gastrointestinal tract for early diagnosis of colon cancer. We are talking about immunochemical tests (for example, Hemoselect kits), which use specific antibodies to human Hb. They make it possible to detect only human Hb in feces, so when using them there is no need for restrictions on nutrition and drug intake. The tests are highly sensitive - they detect even 0.05 mg of Hb per 1 g of feces (usually values ​​above 0.2 mg/g of feces are considered a positive test result). They do not detect bleeding from upper sections Gastrointestinal tract, which allows them to be used specifically for the diagnosis of tumor lesions of the colon. Immunochemical tests are positive in 97% of cases

colon cancer in a single study and in 60% - with adenomatous polyps measuring more than 1 cm. In 3% of cases, tests can be positive in the absence of a tumor in the colon.

The experience of using immunochemical tests in foreign clinics shows that stool testing for occult blood makes it possible to detect colon cancer in the early stages of development and leads to a reduction in mortality by 25-33%. In addition, this test is an alternative to endoscopic (colonoscopy) screening for colon cancer. Regular stool occult blood screening results in a reduction in the detection of colon cancer by last stage development by 50% [Henderson D.M., 1997].

A positive stool reaction to occult blood is possible in many diseases:

Peptic ulcer of the stomach and duodenum;

Primary and metastatic tumors of the esophagus, stomach, intestines, duodenal papilla;

Intestinal tuberculosis, nonspecific ulcerative colitis;

Infestations by helminths 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 with localization of bleeding telangiectasia anywhere in the mucous membrane digestive tract;

Typhoid fever (in patients typhoid fever with positive results of the reaction to occult blood in the stool, macroscopic bleeding occurs much more often than with negative results; although pronounced bleeding is possible without previous hidden ones);

Entering the digestive tract of blood from the oral cavity and larynx, with cracked lips, with accidental or intentional (for the purpose of simulation) sucking of blood from the oral cavity and with its leakage in cases of nosebleeds;

Getting into the feces of blood from hemorrhoids and anal fissures;

Getting into the stool of menstrual blood.

Blood found in feces almost always means the development of a disease in the gastrointestinal tract. Therefore, if it is not detected in a timely manner, it can lead to serious complications. It is worth noting that the smallest particles in blood stool cannot be detected naked eye. But they are the main indicator of the development of a pathological process in the gastrointestinal tract. Helps identify microscopic blood discharge in stool laboratory analysis for occult blood.

It is carried out by taking biological material from the patient and further examining it. Given diagnostic method requires careful and consistent preparation, otherwise the results will be false positive, which will interfere with the procedure correct diagnosis.

We will learn further about what the test for occult blood in the stool reveals, how to prepare for it, and in what cases doctors prescribe the test.

Testing for occult blood in stool is carried out in three ways.

Type of analysis	What it reveals, how it is carried out
Gregersen method (reaction), reaction with benzidine	This test is prescribed to detect bleeding in the upper and lower digestive tract. The reaction occurs both to human hemoglobin and to foreign hemoglobin (contained in meat). Therefore, before performing the analysis, it is recommended to observe strict diet with a complete exclusion of meat products from the diet
Immunochemical analysis	This study gives a more accurate result. Diagnostics, as a rule, is prescribed for suspected development of pathologies of infectious origin in the lower parts of the digestive tract - intestines (this test cannot detect bleeding in the stomach and esophagus) and colon cancer. The sensitivity of the test is so high that it can detect even 0.05 mg of hemoglobin per 1 mg of feces. The only drawback of the study is its length. The result is announced only after 14 days
Guaiac test (Weber test)	When carrying out this diagnosis, particles of the patient's excrement are placed on special filter paper. Guaiac, acetic acid and hydrogen peroxide are then applied to them. This method is still carried out in many laboratories and gives many false reactions. Today there are tests in which guaiac is pre-applied to a strip of plastic. This allows you to detect even the smallest amount of blood in the stool.

Only a doctor should determine what type of research should be performed, depending on the specific case.

Reaction with benzidine in modern medicine used quite rarely. This type of study can detect only 15 ml of blood in excrement. In addition, this diagnosis is characterized by multiple false results.

Attention! Immunochemical tests for the development of oncology in the large intestine are positive in 98% of cases. In the presence of polyposis in the intestines - 60%. Thanks to this diagnostic method, doctors are able to diagnose colon cancer at an early stage, which can reduce mortality from this disease by 25%.

Why does occult blood appear in stool?

The main source of blood excretion in feces is cancer developing in the small or large intestine. At the same time, the forming hemoglobin and red blood cells do not turn red and cannot be detected, even by performing a coprogram.

This is explained by the fact that malignant tumors at the primary stage of development are small in size. When feces move through the intestinal passage, the formation may be slightly injured, releasing a small amount of blood, which penetrates the intestinal duct and is processed by bacterial or digestive enzymes. This process causes the blood to lose its natural color and become transparent. Therefore, no test other than testing for blood hidden in feces will be able to detect it.

What other diseases can be identified using this study?

1. Crohn's disease. This is inflammation in chronic form, which manifests itself in the form of the formation of granulomas - nodules - in various parts of the gastrointestinal tract.

   

2. Erosive and ulcerative lesions in different areas of the intestines and stomach.

   

3. Polyps that form in the epithelium of the colon.

   

4. Inflammation of any origin that injures the intestinal walls.
5. Diverticulosis. This is a disease that is characterized by the appearance of diverticula, or protrusion (in the form of a pouch) of the walls of the large intestine, less often the small intestine.

   

6. Inflammation in a chronic form, leading to pathological processes occurring in the intestinal mucosa.
7. Tuberculosis.
8. Bleeding gums. Typically leads to a false positive result.
9. Cracks in the intestines, inflammation of hemorrhoids (hemorrhoids).
10. Helminthiasis. Infection with invasions that injure the intestinal walls.

Reasons for the presence of occult blood in the stool in children under 3 years of age.

Important! If the results are positive, a repeat test is required. After all, quite often patients violate the preparatory stage, characterized by adherence to a strict diet.

When is a test needed to determine the presence of occult blood in the stool?

The main indication for this study is the patient’s complaints of abdominal pain and general malaise. A gastroenterologist almost always orders this testing to detect malignant and benign processes in the gastrointestinal tract at the initial stage of their development.

What other symptoms are an indication for testing to detect the presence of occult blood in excrement?

1. Soreness, colic, bloating, which immediately disappear after bowel movement.
2. Pain during the act of defecation at the time of straining.
3. A feeling of insufficient emptying of the intestines from feces after bowel movement.
4. Reluctance to eat.
5. Dramatic weight loss.
6. Detection of bloody impurities and mucus in the stool.
7. Often troublesome diarrhea or constipation.
8. Complaints of nausea, vomiting, increased temperature.

Attention! It is recommended to take a test once a year to determine occult blood in feces up to 40 years of age to exclude the development of tumors - malignant and benign.

Preparatory stage

Any study can give false results due to improper preparation for its conduct. Here are the basic rules that will allow you to get the most reliable result.

To take the test, you need to purchase a special sterile container with a plastic spatula from the pharmacy. Parts of excrement are taken from different areas and placed in a container. The biological material is sent to the laboratory within 3 hours.

Important! Many paid laboratories practice stool examination after 3 systematic bowel movements. Each time, excrement particles are taken from different places.

Video - Fecal occult blood test

What the analysis shows

A small amount of blood in the stool is absolutely normal. Its small amount is always found in feces - 1 ml (1 gram of feces accounts for 1 mg of hemoglobin). However, this indicator is considered normal if the specified volume is excreted in excrement per day. No one will pay attention to such a tiny amount of attention, since no one has yet canceled the natural processes in the body.

A positive reaction in the analysis results is marked with a “+” sign. And the more of these marks, the higher the intensity of the reaction. A strongly positive result looks like this: “++++”, a weakly positive reaction – “+”, a positive reaction – “++” or “+++”.

Important! If the reaction turns out to be negative, this does not mean that there is no internal bleeding. After all, this process is periodic. Therefore, they are not always identified during testing.

False positive and false negative reaction

To get the most reliable results, you should follow a nutritious diet. Preparatory stage requires a careful approach, otherwise the analysis will show incorrect results, which will complicate the diagnosis.

If you neglect medical rules, then hemoglobin levels in the absence of gastric or intestinal bleeding will be high. Thus, the reaction with benzidine has hypersensitivity to the iron. And if the patient eats at least one green apple on the eve of the test, this will certainly lead to a false positive result.

Laboratory analysis of stool to determine occult blood helps to recognize gastrointestinal diseases, including malignant processes, at the initial stage of their development. This test is used when conventional research methods are powerless.

In order to determine the condition of the human body, you need to undergo an examination and submit some materials to a laboratory for research. Exists large number types of tests, one of them is feces for occult blood. Preparation takes several days.

Collection of stool for occult blood: indications

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

The reason for the analysis may be:

• Severe intestinal diseases;
• Ulcer;
• Colitis;
• Polyps;
• Anemia;
• Poor appetite;
• Abnormal stool;
• A sharp change in weight downward;
• Frequent constipation;
• Heartburn;
• Acute pain in the abdominal area;
• Constant nausea.

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

You can get a referral for analysis from a surgeon, therapist, oncologist or gastroenterologist.

What do you need to know about the study?

At the present stage, everyone who undergoes an occult blood test needs to have at least general information about this.

The fresher the sample, the more accurate the results will be.

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 of the gastrointestinal tract, less with malnutrition, consumption of protein foods, and 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.

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 for use several hours before sample collection, and special drugs in another 3-4 days. If you break 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, special preparation is needed - following a diet. 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.

The last rule applies to 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:

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

Sample menu for one day:

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

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

Feces for occult blood: interpretation

The finished analysis, interpretation, 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.

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 small internal bleeding. Determination of occult blood in feces is used to diagnose pathological processes in the gastrointestinal tract, when varicose veins esophageal veins, intestinal polyps, gastric 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 medical care. If minor bleeding occurs due to injury to the gastrointestinal mucosa, the coloring and consistency of the 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.

With regular use of this test, the detection of late-stage malignant colon tumors is reduced 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 fecal occult blood test becomes positive, so the test is performed to diagnose polyps, ulcers, diverticula or tumors of the gastrointestinal tract at an early 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 a neoplasm of the gastrointestinal tract (benign or malignant) is diagnosed using an instrumental method, 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 occult blood testing is carried out in morning time(for 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 fecal occult blood test is carried out 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 eat buckwheat, rice porridge, potatoes, butter, bread, and 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 rectum 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. When quantitatively determined, a negative result is 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 for a positive fecal reaction to 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. The vascular network on the surface of a malignant tumor of the small intestine or colon polyp has a fragile structure and is therefore easily injured during defecation. In this case, a small amount of blood enters the stool, which cannot be visually determined.

Treatment of abnormalities

Fecal occult blood analysis is considered a common medical test, 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, CBC with leukocyte count and ESR, fecal examination for Giardia, scraping for enterobiasis. To adjust the indicators during re-analysis, it is important to adhere to a special diet and refrain from taking medications (vitamin C, aspirin, bismuth and iron preparations).

Blood in the stool can be hidden, invisible to the eye, and can only be detected with the help of special tests.

The presence of occult blood in the stool indicates small, slow periodic bleeding in the digestive tract. This loss of blood is most often asymptomatic and does not allow the nature and location of bleeding to be determined. Every part of the digestive tract can be the site of hidden bleeding, and diseases can range from benign (hemorrhoids) to the much more serious tumors.

Hidden blood and cancer

The occult blood test is an important test for colorectal cancer screening and timely treatment. WHO recommends that for screening for colorectal cancer in men and women aged 50 to 70-74 years, fecal occult blood testing is performed once a year. If the test is positive, the patient undergoes a colonoscopy.

Early diagnosis colorectal cancer is very important because patient survival is related to the stage of their disease at the time of diagnosis; 94% survive for 5 years with localized disease, and only 9% - if the disease is in the metastatic phase.

The occult blood test is based on the assumption that early tumors and small adenomatous polyps usually do not produce any symptoms but may bleed periodically. This minimal bleeding can be detected by the test and serve as the start of targeted diagnostic procedures.

Occult blood test

Two tests are used to detect occult blood in stool: Guaiacol (gFOBT) and immunochemical test (FIT = iFOBT).

In the chemical test, guaiacol uses chemical substance, which reacts with hemoglobin peroxidase (Hb) of red blood cells. The reaction is unfortunately positive with non-hemoglobin peroxidase of food origin, which can give a false positive result. The test does not reveal the location of the bleeding.

To avoid false results when performing a guaiacol test, the patient is recommended to:

1) avoid eating raw or lightly processed red meat and all types of fish, turnips, horseradish, antioxidants (eg iodine and boric acid),

2) avoid foods rich in vitamin C, alcohol, medications containing iron;

2) avoid situations that could lead to bleeding ( dental procedures, taking medications that can cause gastrointestinal bleeding - anticoagulants, aspirin; It is also important to brush your teeth gently so as not to cause bleeding gums.

To increase the diagnostic sensitivity of the guaiacol test, three stool samples are usually collected on three different days.

Immunochemical test or "test second generation" reacts only with human heme globin. In addition, the immunochemical test detects hidden blood from the lower intestines - the colon and rectum (polyps, tumors, angiodysplasia, diverticulosis, hemorrhoids, fissures, etc.).

The immunochemical test is characterized by high sensitivity (fewer false negatives) and specificity (fewer false positives) compared to the Guaiac test. The test does not require dietary restrictions.

If the occult blood test is positive

About 5-6 people out of 100 test positive for occult blood, but this does not necessarily mean polyps or colon cancer are present. The test is positive for hemorrhoids, ulcers, fistulas, diverticula, angiodysplasia, inflammatory diseases, etc. Therefore, if the test is positive for a correct diagnosis, it is important to perform colonoscopy.

If the occult blood test is negative

Polyps and tumors at an early stage bleed periodically, so it may happen that the first test, even in the presence of a lesion, is negative. Therefore, to increase the likelihood of detecting existing bleeding, it is recommended to repeat the test periodically. The optimal frequency, given the slow development of polyps and their malignant transformation, is once every two years using an immunochemical test and annually with the Guaiac test

ATTENTION: if the test is negative, you still need to go to the doctor if you have persistent constipation or persistent diarrhea, the presence of red or black stool; feeling of discomfort in the rectum after defecation; sudden weight loss without reason, nighttime abdominal pain

Notes:

The occult blood test is performed only 3-5 days after the end of menstruation

For constipation, a blood test does not exclude the use of laxatives.

With red and black stools ( visible to the eye bleeding) it is not logical to perform an occult blood test.

If the occult blood test is positive, alternative tests may be performed instead of a colonoscopy, but colonoscopy is preferable because it allows for a biopsy and removal of the polyps, called a polypectomy.

Some tips for performing the occult blood test correctly

• Collect feces in the morning
• Collect feces so that they do not get into the water. It is advisable to collect it in a clean, dry container, or cover the toilet with film so that the feces end up on the film. Urine should not go into feces!
• Specimens should not be collected within three to five days after the end of menstruation if there is hemorrhoidal bleeding. Alcohol, aspirin and other anti-inflammatory drugs can cause irritation of the intestines (including the colon) and cause hidden bleeding. The sample is collected with a special spatula in a jar, with 3-4 different points surface of stool.
• If three stool samples are needed for research, they must be collected from three bowel movements, even on the same day.
• Stool can be delivered to the laboratory within a few hours
• If three samples need to be collected, each collected sample is stored in a refrigerator and then transported to the laboratory at the same time
• Once collected, occult blood samples are stable for a maximum of 7 days. But the requirements of the laboratory should be taken into account.

So, the test for occult blood in stool is of fundamental importance in screening for colorectal cancer, since tumors are asymptomatic, but can be detected and treated in time only due to their minimal, even periodic bleeding,

Hidden bleeding often manifests itself as a clinical picture of anemia (hypochromic, microcytic anemia). Therefore the presence clinical picture anemia, targeted studies should be carried out (gastroscopy, colonoscopy, etc.) and feces for occult blood.