Why donate feces for occult blood. Deciphering the analysis of feces for occult blood. What to do if the test is positive

An analysis for occult blood in the feces is a laboratory method for studying biomaterial by certain chemical reactions, the accuracy of which depends on the careful preparation of the patient for diagnosis.

Therefore, it is important to know how to properly prepare and take this analysis, for which it is necessary, which shows the identification of invisible, latent blood.

Causes of blood in the stool

The main reason for the appointment of the analysis is the suspicion of bowel cancer, any of its departments. Indeed, very often the onset of a terrible disease passes without obvious symptoms and bleeding.

The presence of blood cannot be seen, not only visually, but even with a microscopic examination.

At the very beginning, a malignant tumor is so small that it is slightly injured during the passage of feces. Very little blood is released, in the intestine it is exposed to the action of enzymes, as a result of which erythrocytes and hemoglobin become colorless, lose their characteristic red tint, and are invisible when emptying. It is impossible to determine them, except by using special chemical reagents. During chemical reactions, red blood cells turn bright colors.

In addition, the test shows positive results in the following cases:

• the formation of polyps in the intestine;
• inflammation that destroys the walls of the digestive tract;
• chronic diseases of any part of the gastrointestinal tract;
• ulcerative colitis or erosions in the intestinal ducts;
• pathologies of the colon, chronic inflammatory processes of the mucous membrane;
• diverticulosis.

A false positive result in a fecal occult blood test can even cause bleeding gums.

What is this research and what is it for?

Compared to instrumental methods, it is completely harmless and painless. But nevertheless, it is very effective, it allows you to finally make sure of the correct diagnosis and begin treatment of a cancerous tumor at the earliest stages of its development, thereby saving the patient's life.

Therefore, it is necessary to treat it with all the responsibility and in no case ignore the appointment of a doctor.

Patients usually complain of the following symptoms:

• pain, bloating, gas formation, passing after defecation;
• problems with stools, constipation or diarrhea, pain when going to the toilet, feeling that he has not cleared feces;
• in the stool there is blood, mucus, foam;
• weight drops sharply, you do not want to eat;
• body temperature rises, accompanied by chills, nausea, and often vomit;
• other problems of the digestive tract.

A fecal occult blood test should be performed after the age of forty for absolutely everyone for safety and early diagnosis of cancer cells in the colon or duodenum.

He also gives up if the general analysis did not reveal blood, and the presumptive diagnosis suggests otherwise.

How is fecal occult blood testing done?

Modern diagnostic centers carry out such diagnostics in two ways:

1. Gregersen reaction (Gregersen) or benzidine test- involves special training, which includes a diet without meat, since chemical reagents determine the red blood cells of not only humans, but also animals. The study of feces by this method allows you to determine hidden bleeding in any part of the gastrointestinal tract.
2. Analysis of feces for occult blood by immunochemical method- the most modern, not requiring to limit products containing iron and meat, reagents determine only human hemoglobin. It is prescribed to clarify the pathologies of the lower part of the digestive tract. But it is not very informative for the stomach and esophagus.

Sometimes laboratories use azopyram tests to detect high levels of red blood cells in stool or urine.

The method of laboratory research is chosen by the attending physician based on the history and complaints of the patient.

Where to do

A stool test for occult blood can be taken at a polyclinic at the place of residence or at paid diagnostic centers.

Depending on the choice of method, its cost ranges from 350 to 700 rubles.

Express analysis for the detection of hidden bleeding can be carried out at home. To do this, any pharmacy sells a special test that works according to the immunochromatographic method and allows you to immediately detect the presence of blood in the stool.

The method of conducting the analysis yourself:

1. Buys a test at a pharmacy.
2. We open, take out a special spatula and a container with a chemical reagent.
3. We collect feces in a container, as written in the instructions.
4. A few drops of the resulting mixture are dripped onto the indicator.
5. You need to wait a bit for the end of the result.
6. With almost 100% probability, two test strips show a positive result. And this means that you need to pay a visit to the doctor.

After 40 years, such a test should be carried out at least once every two years, and after fifty - once a year is mandatory.

Preparation for analysis

The immunochemical method eliminates the diet, so you can eat everything. But in 14 days, refuse:

• any laxatives;
• drugs such as Aspirin or Ibuprofen that affect blood clotting and cause bleeding;
• instrumental diagnostic methods such as colonoscopy or barium enema, which can change the intestinal mucosa. This should also include enemas and rectal suppositories.

The Gregersen reaction requires more careful preparation. Otherwise, a false positive result can be obtained, since the reagents are sensitive to animal hemoglobin, some vitamins and other substances contained in food.

Many patients are interested in the question of how long it takes to prepare for this procedure and how to do it.

Preparation for the study begins 3-4 days in advance and includes:

• diet
• complete rejection of medications containing bismuth, iron-containing components, ascorbic acid, acetylsalicylic acid and barium;
• transfer of instrumental diagnostics of the intestine for several days after the test. It is forbidden to conduct a colonoscopy or x-ray the day before;
• exclusion of rectal suppositories and enemas;
• refusal to brush your teeth and visit a dentist, since blood during bleeding gums during the treatment period can enter the gastrointestinal tract and give a false result.

Note!

Women during the menstrual cycle should not be tested for fecal occult blood.

Prohibited Products

What can not be eaten and should be excluded from the diet 4 days before the test:

• meat and offal, including liver;
• fish meals;
• sausages, ham;
• apples in any form, especially green;
• plums, bananas, pineapples;
• from vegetables - tomatoes, carrots, beets, bell peppers, cucumbers, cabbage of any kind, zucchini;
• dishes from foods containing a large amount of iron, as well as blueberries, pomegranates, white beans.
• paprika, any fresh herbs, horseradish, nuts.

What you can eat:

• eggs in any form;
• cereals;
• potato;
• bakery products;
• butter, including butter;
• fruit, but not too much;
• dairy and dairy products.

How to pass the analysis

The accuracy of any method depends not only on the preparation, but also on how correctly the feces are collected. When sampling material, impurities in the form of droplets of water or urine, vaginal discharge, drug residues, suppositories, laxatives, etc. should be avoided.

In the pharmacy, you should purchase a plastic disposable sterile container with a tightly screwed lid. It is equipped with a special spatula

How to make a fecal collection yourself:

• you can’t empty yourself into the toilet, so take care of a special container in advance;
• take, for example, a pot, wash thoroughly with soap or other cleaning antibacterial agent, rinse several times with running water, treat with boiling water;
• the process of defecation should not be accompanied by the release of urine, so first empty the bladder;
• stools for analysis must be obtained naturally. Do not give enemas or take laxatives;
• after defecation in a pot, separate at least a teaspoon of feces with a spatula and transfer to a special container. The mass should not occupy more than a third of its volume;
• for more accurate results, several stool samples can be taken from different parts of the feces into different containers;
• screw tightly, attach a direction and take it to the laboratory.

How to submit:

• feces you must bring to the laboratory fresh, its storage period is no more than 3 hours;
• for a while you can still store it on the refrigerator shelf, but then you have to deliver the biomaterial, overlaid with ice cubes and urgently by taxi;
• frozen or preserved biomaterial is not suitable for diagnosis.

The terms depend on the laboratory you applied to, and range from three to six days.

Deciphering the results: the norm and possible diseases

A negative result is normal for the human body. But it does not always carry informative accuracy. In this case, repeated tests are usually prescribed. A negative result does not always indicate that there are no internal bleeding in the digestive tract.

A positive result indicates an excess of blood in the feces, the norm of which is no more than 2 mg of hemoglobin per 1 g of biomaterial.

The intensity of chemical reactions is expressed from one to four pluses. One is a weakly positive result, the rest are positive.

Gregersen's analysis is positive - what does it mean:

• malignant tumors in any of the gastrointestinal tract;
• the presence of polyps and erosion;
• exacerbation of an ulcer;
• hemorrhoids;
• varicose veins in the digestive tract;
• intestinal tuberculosis;
• Crohn's disease.

The source of selections must be determined additionally.

Note!

The presence of latent blood in the feces does not always indicate the pathology of the digestive organs.

False results

If the patient, when prescribing the Gregersen method, did not follow a strict diet, then most often the result of the analysis is false positive, as in the following cases:

• nosebleeds;
• monthly;
• bleeding gums;
• helminthiasis;
• diseases of the hematopoietic organs.

In a newborn baby, a baby, a false positive reaction is often associated with the presence of allergic reactions and constipation.

What does the decoding of the results of the immunochemical method say?

The answer to the question will be a hemoglobin content of more than 50 ng / ml. This means inflammatory processes in any of the sections of the intestine, damaging the walls of the mucosa. At this point, a large number of red blood cells are present in the blood. Can mean:

• chronic diseases of any part of the gastrointestinal tract, called Crohn's disease;
• malignant processes in the large intestine;
• hemorrhoids;
• ulcerative inflammation of the large intestine

Fecal occult blood analysis is considered a fairly informative method, but despite this, it is often false positive or false negative. It depends on many factors that an experienced doctor will definitely foresee. He will prescribe a second test, and even better, conduct a colonoscopy, which is more likely to help confirm or refute the preliminary diagnosis.

Pathologies of the duodenum, stomach, esophagus may be accompanied by internal bleeding. Stool analysis helps to identify them at an early stage. The study reveals occult blood, which often becomes a sign of cancer.

What is occult blood in stool

Traces of blood that are invisible to the human eye in excrement are called occult blood. They are found only during special tests for the detection of transferrin or hemoglobin. The study gives the most reliable results in identifying such pathological conditions:

• duodenal ulcer, stomach;
• helminths in a child;
• tuberculous lesions of the intestine;
• blood diseases;
• varicose veins of the esophagus;
• Crohn's disease;
• erosive esophagitis;
• cirrhosis of the liver;
• Lynch syndrome;
• hemorrhagic diathesis;
• tumors;
• polyposis;
• inflammation of the palatine tonsils, pharynx.

Analysis of feces allows you to detect colorectal cancer, intestinal tumors at an early stage. Positive test results are typical for such pathologies:

• diverticula of the intestine, stomach;
• erosive gastroduodenitis;
• nonspecific ulcerative colitis;
• damage to the mucous membrane of the digestive system.

When is an occult blood test ordered?

Doctors prescribe a fecal examination to the patient when signs of diseases of the digestive system appear. Indications for the study are the following symptoms:

• abdominal pain of unknown etiology;
• false urge to defecate;
• causeless loss of body weight;
• diarrhea;
• constipation;
• hyperthermia;
• nausea;
• heartburn;
• vomit.

Methods for detecting occult blood in feces

When internal bleeding is suspected, doctors use different methods for examining feces. They differ in sensitivity, efficiency, the need for preparation, the definition of pathologies in various parts of the intestine. Diagnostic methods for occult blood, their advantages and disadvantages:

Benzidine test

This analysis of feces for the detection of hidden blood loss has a second name - the Gregersen test. The main reagent is benzidine, to which acetic acid and barium peroxide are added to increase activity. The technique gives a lot of false positive results - a reaction to nosebleeds, eating meat, drugs, bleeding gums.

Immunochemical test

Operative research reveals neoplasms in the colon at an early stage, reduces cancer mortality by 30%. Immunochemical analysis of feces for occult blood reacts only to human protein, does not require special preparation. It is characterized by high sensitivity and such features:

Guaiac test

The sensitivity of the guaiac test depends on the concentration of hemoglobin. If its content is more than 2 mg per gram of feces, the result is positive in 90% of cases. The test diagnoses bleeding in any part of the digestive system. The analysis has the following specifics:

Rules for preparing for the study

To obtain an accurate test result, proper preparation is essential. The process begins a week before the analysis, includes the following activities:

Features of preparing for the Gregersen test

To eliminate the error in the results of this technique, it is important to strictly follow the diet. The Gregersen test for occult blood is sensitive to iron, pigments from food. It is necessary to postpone research for a while under the following circumstances:

• the presence of blood in the urine (hematuria);
• menstruation in women;
• hemorrhoids with bleeding;
• periodontal disease;
• indigestion (dyspepsia);
• breaks, damage as a result of anal sex.

An important role is given to the correct sampling of material for analysis. The following conditions must be met:

• conduct hygiene of the genitals, anus;
• collect feces in the morning, before breakfast;
• ingress of water, urine is unacceptable;
• you can not take biomaterial from the toilet (you need to put an oilcloth);
• fragments must be from three places;
• put the feces in a special sterile container;
• deliver to the laboratory within two hours.

Deciphering the analysis of feces for occult blood

The physician interprets the test results. The immunochemical test is considered the most accurate, but it is not performed in all laboratories. It takes 1-3 days to conduct and decipher the analyzes. Experts recommend, upon receipt of positive and negative results, to conduct an additional re-examination of feces for the presence of hidden bleeding and diagnostics using instrumental methods.

Negative result

If a small amount of blood enters the intestines, in a healthy person, under the action of enzymes, it decomposes. The norm is 0.2 mg of hemoglobin per gram of feces. A negative result confirms the absence of bleeding in the body, dangerous diagnoses, or requires a second examination when the patient has signs of pathologies.

Positive

If a patient is suspected of having occult bleeding, a positive test result is possible. Often it indicates an early stage of diseases associated with damage to the mucous membranes:

• colorectal cancer;
• peptic ulcer;
• intestinal tuberculosis;
• tumors of the digestive system;
• helminthiasis;
• pathologies of the veins of the esophagus;
• hemorrhoids.

Positive test for occult blood in a child

When analyzing feces in children, signs of hidden bleeding are sometimes revealed. The reason for a positive reaction depends on age:

False positive and false negative results

Often, studies of feces for the presence of hidden blood loss give ambiguous results - false negative, false positive. In this case, it is necessary to perform repeated analyzes, conduct additional diagnostics. A false positive response is possible in such cases.

A test for occult blood in the feces is prescribed if occult bleeding is suspected. Normally, 1 g of feces of a healthy person contains no more than 2 mg of hemoglobin, that is, less than 2 ml of blood is excreted with feces during the day. With significant gastrointestinal bleeding, the color of the stool changes.

With a high localization of the source of bleeding (stomach, duodenum, small intestine), they become dark, tarry (melena), and with low blood in the feces, it is detected visually. If blood is present in the feces, but is not determined either visually or during microscopy, it is called latent, and the bleeding, respectively, is latent. It can be detected by laboratory methods of fecal occult blood analysis:

• test with benzidine (Gregersen reaction) or guaiac resin;
• quantitative immunochemical method.

Detection of blood in the feces indicates that the patient has diseases of the stomach or intestines that occur with a violation of the integrity of their mucous membrane.

Causes of gastrointestinal bleeding

The following diseases lead to the development of bleeding from the organs of the gastrointestinal tract (GIT):

• peptic ulcer of the stomach and duodenum;
• polyps, benign and malignant tumors of the digestive tract;
• diffuse familial polyposis;

Patients suffering from these diseases should be regularly tested for occult blood in the feces.

After reaching the age of 50, each person is recommended to take a fecal occult blood test annually, it is included in the algorithm for early diagnosis of malignant neoplasms of the intestine, the incidence of which at this age increases significantly. The appearance in adults, especially older than 50 years, of a positive test for fecal occult blood is the basis for further in-depth examination.

Benzidine test

Benzidine test (Gregersen-Adler reaction) is a chemical reaction used to detect blood impurities in biological material (urine, gastric juice, feces). In the presence of blood, after adding the reagent, the color of the test material becomes bright green or blue.

This analysis requires the preparation of the patient, since it is possible to obtain a false positive result due to hemoglobin contained in meat food, some vitamins and other substances.

To exclude a false positive result, you must follow a diet. 72 hours before the study, food of animal origin (fish, poultry, meat) and some vegetables (tomatoes, zucchini, herbs, green apples, horseradish, cucumbers, cauliflower, broccoli) are excluded from the diet.

In infants, the cause of a false positive result may be cracked nipples in the mother. During feeding, these cracks bleed, and the children swallow the secreted blood along with breast milk.

Diet in preparation for the study:

• dairy products (ryazhenka, kefir, cheese, cheese, cottage cheese, milk);
• cereals (oatmeal, rice, millet);
• vegetables (potatoes, carrots, white cabbage);
• fruit;
• weak tea, mineral water without gas;
• sweets and confectionery.

Immunochemical analysis of feces for occult blood

Old methods for determining occult blood in feces, including the benzidine test, react not only to human hemoglobin, but also to animal hemoglobin contained in meat products, so it is not always possible to accurately determine what a positive result shows - occult bleeding or errors nutrition.

The immunochemical method is devoid of this drawback and reacts specifically to human blood. This means that it does not require the patient to follow a special diet.

Rules for collecting material for occult blood testing

Three days before the test, you should stop taking iron and bismuth preparations, and one day - vitamin C (ascorbic acid) and Aspirin (acetylsalicylic acid).

72 hours before the study, it is necessary to exclude any diagnostic or therapeutic manipulations affecting the organs of the gastrointestinal tract, that is, colonoscopy, sigmoidoscopy, X-ray contrast examination of the digestive tract should not be performed.

The day before the fecal occult blood test, the patient is not recommended to brush his teeth, as a brush, especially with hard bristles, can injure the gums, causing them to bleed.

Feces for research should be taken only after self-defecation. It is unacceptable to take laxatives or enema before the study, as this distorts the result.

With a high localization of the source of bleeding, the feces become dark, tarry in color, and with a low localization, blood in the feces is detected visually.

Care must be taken to prevent urine or vaginal discharge from entering the material by urinating before defecation, then washing and drying the perineum with a towel. During bowel movements, you should not strain excessively.

Immediately after defecation, material is taken from 3-4 areas of stool and placed in a disposable container with a lid and a spatula, which is obtained in advance from the laboratory or purchased from a pharmacy. 1/3 of the container is enough for research. The collected material must be delivered to the laboratory as soon as possible.

Deciphering the analysis of feces for occult blood

Normally, blood should not be detected in the feces. The following factors can lead to false results:

• non-compliance by the patient with the prescribed diet (when setting a benzidine test);
• collection of analysis on the days of menstruation in women;
• high bleeding gums.

In infants, the cause of a false positive result may be cracked nipples in the mother. During feeding, these cracks bleed, and the children swallow the secreted blood along with breast milk.

The immunochemical method can also give false negative results. This is observed in cases where fresh unchanged red blood cells are present in the feces, for example, with bleeding anal fissures or external hemorrhoids.

If all the rules for preparing and collecting a fecal occult blood test were followed, and factors affecting its reliability were excluded, the detection of blood in it indicates that the patient has diseases of the stomach or intestines that occur with a violation of the integrity of their mucous membrane:

• nonspecific ulcerative colitis;
• Crohn's disease;
• colorectal carcinoma;
• peptic ulcer of the stomach or duodenum;
• intestinal tuberculosis;
• haemorrhoids.

If there is doubt about the reliability of the results of the analysis, it is done again.

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Few, having emptied their intestines, think that the characteristics of this biomaterial can be used to judge the presence of such serious pathologies as stomach ulcers, Crohn's disease, polyps and malignant neoplasms of the intestine.

To identify them, you will need to take fecal occult blood tests. 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 in the feces with the naked eye.

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 feces may turn black - this is an 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 see them with a microscope. It is this blood that is called latent.

It can be found in feces in the following ways:

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

Chemical samples

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. Reacting with substances such as benzidine and guaiac, it changes their color. The more occult blood in the feces, the more intense and faster the color of the reagents changes.

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

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

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

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

Method of immunochromatography

More perfect immunochemical analysis of feces. It is convenient, standardized and simple. Immunochromatographic detection of occult blood resembles the procedure for performing a pregnancy test.

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

The monoclonal particles bind to human hemoglobin to form a colored complex. Further, it is captured by other antibodies localized in the control region, and two marks appear on the test strip if the concentration of occult blood is higher than normal. Otherwise, one bar is rendered.

The immunochemical method is highly sensitive and does not require special preparation. It allows you to detect weak bleeding in the early stages of colon cancer in 97% of cases. However, the analysis is not suitable for diagnosing diseases that develop in the small intestine.

Fluorescence analysis

Fluorescence can also be used to detect hemoglobin breakdown products in feces. 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 food the day before, animal hemoglobin will appear in his feces - this will cause a false result.

Recently, another approach to diagnostics has been developed. Human DNA is extracted from the feces selected for analysis and examined for changes characteristic of the tumor process.

When should I take a fecal occult blood test?

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

• heartburn;
• stomach ache;
• change in the nature of the chair;
• nausea or vomiting that bothers you for a long time;
• mucus impurities in the feces;
• foamy inclusions.

In addition, an occult blood test should be performed annually for all persons over the age of 40 years. 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;
• loss of appetite;
• aversion to meat food;
• sudden loss of body weight;
• constipation;
• pain during defecation.

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

How to prepare for the analysis?

To pass a stool test for occult blood, special preparation will be required. Depending on which method or methods of research will be used, the patient will have to adhere to a certain regimen.

Diet

Chemical assays and fluorescent analysis are non-selective. They detect components of not only human, but also animal hemoglobin obtained from food. For this reason, before such an analysis of feces for occult blood, a diet is shown that implies a complete rejection of meat, fish, and poultry. Any by-products are also prohibited.

In addition, when preparing for a fecal 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 by immunochromatography, the need for a special diet disappears. Monoclonal antibodies bind exclusively to human hemoglobin and do not react to compounds of a different origin.

Medicines and medical procedures

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

During this period, you should refrain from any procedures that are theoretically capable of violating the integrity of the intestinal and stomach mucosa. You can not put enemas, undergo fibrogastroscopic examination, undergo irrigoscopy, sigmoidoscopy, colonoscopy. Even laxatives are banned. You need to stop taking them at least a week before the analysis.

From the moment of the last x-ray examination to the moment when the feces are collected for analysis, at least 3 days must pass.

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, you should refrain from brushing your teeth on the eve of the analysis, because bleeding from the gums is not uncommon.

Women should not take feces for analysis during menstruation. Even nosebleeds that occurred the day before can distort the results. In addition, when taking the material, it is important to ensure that urine does not get into it.

Features of the collection of biomaterial

Feces for analysis are taken into a sterile special container. You can buy it at a pharmacy.

• It is necessary to collect biomaterial from different parts of the feces: 2-3 fragments.

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

The less time that has passed since collection, the better.

Deciphering the analysis of feces for occult blood

Immunochemical analysis and samples with benzidine and guaiac are semi-quantitative methods for the determination of occult blood. The first diagnosticum gives an answer to the question: does the concentration of hemoglobin in the stool sample exceed the normal value?

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

When setting samples with guaiac and benzidine, the intensity and speed of staining of the reagents are evaluated. 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 concentrations of porphyrins up to 2 mg/g of biomaterial. But when their content in 1 g of feces is equal to or exceeds 4 mg, a pathology is diagnosed. The test is also able to reveal borderline values: from 2 to 4 mg.

The analysis is positive, what does it mean?

Having received the conclusion that occult blood was detected in the stool sample, you should not panic. In addition to pathological conditions, the result can be positive in the following cases:

• non-compliance with the rules of preparation for analysis;
• nose bleed;
• menstruation;
• stomatitis;
• periodontitis.

If occult blood is detected, the doctor will refer the patient for additional examination. Colonoscopy will allow you to assess the condition of the mucous membrane of the large intestine, to identify foci of altered cells (polyps and tumors).

If necessary, a biopsy of pathological material is performed. In addition to colonoscopy, computed tomography and magnetic resonance imaging (CT and MRI) are used.

A positive analysis of feces for occult blood occurs with helminthiases, ulcers of the stomach and small intestine, Crohn's disease, colitis, intestinal tuberculosis, hemorrhoids, anal fissures, as well as with polyps and tumors.

The latter may not cause permanent bleeding and can be detected only with a systematic diagnosis. It is desirable to conduct at least 3 consecutive studies.