Why is an occult blood test needed? How to correctly test stool for occult blood using various methods of stool examination.
Description:
Blood in the stool, a condition also known as bloody stool, occurs when blood from the gastrointestinal tract enters a person's stool. The presence of blood in the stool can be caused by a number of conditions, ranging from colon cancer.
Causes of blood in stool:
Most often, blood in stool is found in the following cases:
1. Stomach ulcer. Stomach bleeding is usually caused by gastritis or peptic ulcer. The blood entering the stomach is black in color, which is due to the oxidation of heme. NSAIDs, such as ibuprofen, aspirin, and naproxen, are common causes of stomach bleeding even when there is no ulcer. In addition to blood in the stool, ulcer symptoms include gastroesophageal reflux, coffee-colored vomit, burning pain in the upper belly. Complications associated with ulcers include anemia and gastric perforation. The latter condition is a medical emergency.
2. Inflammatory bowel diseases. Intestinal bleeding can have a variety of causes, the most common being inflammatory bowel disease (IBD). These diseases include Crohn's disease and peptic ulcer, both of which can cause blood in the stool. Blood from the intestine may be dark or bright red, depending on the location of the defect in the intestinal wall. Other symptoms of IBD include diarrhea, weight loss, vomiting and abdominal pain. Although IBD is generally not a fatal disease, if left untreated, there is a high incidence of morbidity (including in the rectum).
3. Hemorrhoids. Hemorrhoids affect the veins in the anus or rectum. Hemorrhoids are one of the most common causes of bleeding from the lower gastrointestinal tract. Blood caused by hemorrhoids is usually bright red in color and may be present on toilet paper as well as in stool. An anal fissure -- a tear in the tissue in the anus -- can also cause bleeding, similar in appearance to that of hemorrhoids. Symptoms of hemorrhoids include pain and itching in the anus, lumps in the anal area, and pain during bowel movements. Pain from hemorrhoids usually intensifies when sitting and during bowel movements.
4. . Sometimes blood in the stool can indicate serious illnesses such as cancer. While the tumor can be located anywhere in the digestive tract, bleeding is most often caused by cancer of the colon (including the rectum). Caused by cancer can vary in color from black (stomach) to bright red ( lower intestine, rectum). Additional symptoms of colorectal cancer include sudden weight loss, changes in eating habits, fatigue and weakness. Most people do not experience any symptoms until the disease progresses beyond the early stages, making early detection increasingly important.
Fecal occult blood test:
Fecal occult blood test - also known as FOBT - is a laboratory test that is used to test stool samples for occult blood. Occult blood in stool may indicate colon cancer or polyps in the colon or rectum - although not all cancers or polyps bleed. Typically, occult blood is present in such small quantities that it can only be detected by the chemicals used in this laboratory test. If blood is found in the stool, additional tests are needed to determine the source of the bleeding. A fecal occult blood test can only detect the presence or absence of blood. Stool occult blood does not indicate potential sources of bleeding.
Your doctor may recommend a fecal occult blood test in the following cases:
- for colon cancer;
- The patient's age is 50 years or older and there is a risk of developing colon cancer;
- to determine the source. Sometimes stool occult blood testing is used to determine gastrointestinal bleeding. Conditions such as bleeding ulcers contribute to anemia.
Various foods, dietary supplements, and medications can affect the results of a fecal occult blood test. This is manifested by false positive or false negative results. To obtain an accurate analysis result, you must follow some rules. For about three days before the test, you should avoid certain foods (certain fruits and vegetables, including broccoli, turnips, red meat, horseradish), medications (vitamin C, aspirin, ibuprofen).
Interpretation of fecal occult blood test results:
Negative result. A stool occult blood test is considered negative if no traces of blood are found in the stool samples. If a stool occult blood test was ordered to rule out colon cancer, your doctor may recommend a repeat test after some time.
Positive result. A stool occult blood test is considered positive if traces of blood are found in the stool samples provided. In the future, additional research may be needed, for example, to find the source of bleeding. It is important to remember that false negative and false positive results are possible. Some cancers and most polyps do not bleed, which can lead to false negative results. Additionally, hidden bleeding can come from other sources, such as stomach ulcers, hemorrhoids, or even ingestion of blood from a nosebleed.
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, bell peppers and green vegetables are also prohibited.
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. It is cleansed of harmful substances, components that can 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.
This technique has no contraindications, but in the presence of 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.
Pathologies of the duodenum, stomach, and esophagus may be accompanied by internal bleeding. Stool analysis helps identify them at an early stage. The study detects occult blood, which often becomes a sign of cancer.
What is occult blood in stool
Traces of blood in excrement that are invisible to the human eye are called occult blood. They are detected only when special tests are carried out to detect transferrin or hemoglobin. The study gives the most reliable results in identifying the following pathological conditions:
- ulcer of the duodenum, stomach;
- helminths in a child;
- tuberculosis 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 tonsils, pharynx.
Stool analysis can detect colorectal cancer and intestinal tumors at an early stage. Positive test results are typical for the following pathologies:
- diverticula of the intestine, stomach;
- erosive gastroduodenitis;
- nonspecific ulcerative colitis;
- damage to the mucous membrane of the digestive organs.
When is an occult blood test prescribed?
Doctors prescribe a stool test for patients when signs of digestive system diseases appear. Indications for research 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 stool
If internal bleeding is suspected, doctors use different methods of examining stool. They are distinguished by sensitivity, efficiency, the need for preparation, and the identification of pathologies in various parts of the intestine. Diagnostic methods for occult blood, their advantages and disadvantages:
| Benzidine test |
| required:
|
| Immunochemical test |
|
|
| Guaiac test |
|
|
Benzidine test
This stool test to detect hidden blood loss has a second name - Gregersen's test. The main reagent is benzidine, to which acetic acid and barium peroxide are added to increase activity. The technique gives many false positive results - a reaction to nosebleeds, eating meat, drugs, bleeding gums.
Immunochemical test
Surgical research detects tumors in the colon at an early stage and reduces cancer mortality by 30%. Immunochemical analysis of feces for occult blood reacts only to human protein and does not require special preparation. It is characterized by high sensitivity and the following features:
Guaiac test
The sensitivity of the guaiac test depends on the hemoglobin concentration. 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 research
To obtain an accurate test result, proper preparation is important. The process begins a week before the analysis and includes the following activities:
| Time to study | What to do | |
| affect intestinal motility |
|
| stop taking:
| change the color of stool |
|
| don't have anal sex | possible damage to mucous membranes |
|
| remove from diet:
| include iron, pigments |
|
| exclude fish, meat, offal (for guaiac or benzidine testing) | ||
| Deadline for performing a stool test:
|
|
|
| possible injury to the gums, blood getting into the stool |
Features of preparing for the Gregersen test
To exclude errors in the results of this method, it is important to strictly follow the diet. Gregersen's reaction to occult blood is sensitive to iron, pigments from food. It is necessary to postpone research for a while under the following circumstances:
- presence of blood in the urine (hematuria);
- menstruation in women;
- hemorrhoids with bleeding;
- periodontal disease;
- indigestion (dyspepsia);
- ruptures, damage as a result of anal sex.
An important role is played by the correct collection of material for analysis. The following conditions must be met:
- carry out hygiene of the genitals and anus;
- collect feces in the morning, before breakfast;
- ingress of water and urine is unacceptable;
- you cannot take biomaterial from the toilet (you need to put an oilcloth on it);
- fragments must be from three places;
- put the feces in a special sterile container;
- deliver to the laboratory within two hours.
Interpretation of stool occult blood test
The doctor interprets the results of the study. 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 tests. Experts recommend that, upon receipt of positive and negative results, additional re-examination of stool for the presence of hidden bleeding and diagnosis using instrumental methods.
Negative result
If a small amount of blood enters the intestines, in a healthy person it is decomposed by enzymes. 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 repeated testing when the patient exhibits signs of pathologies.
Positive
If a patient is suspected of having hidden bleeding, a positive test result is possible. It often indicates an early stage of diseases associated with damage to the mucous membranes:
- colorectal cancer;
- peptic ulcer;
- intestinal tuberculosis;
- tumors of the digestive organs;
- helminthiasis;
- pathologies of the esophageal veins;
- hemorrhoids.
Positive reaction to occult blood in a child
When analyzing stool 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, stool examinations for the presence of hidden blood loss give ambiguous results - false negative, false positive. In this case, repeated tests must be performed and additional diagnostics carried out. A false positive response is possible in such cases.
A stool occult blood test detects even a small amount of blood, makes it possible to detect diseases in the primary stages, and this increases the likelihood of a favorable outcome. In the initial stages, the pathology is asymptomatic, and it is impossible to independently detect internal bleeding. Biological fluid in feces can indicate a dangerous disease - from hemorrhoids to malignant neoplasm.
- colorectal cancer;
- abnormal growth of tissue over the mucous membrane of the large intestine;
- ulcers, stomach erosions;
- diverticular disease of the colon;
- granulomatous enteritis;
- inflammatory processes that damage the inner lining of the intestine;
- haemorrhoids;
- nonspecific ulcerative colitis.
In young children, this may be due to individual sensitivity to cow's milk. If the baby is breastfeeding, then the mother's consumption of dairy products is to blame for the bleeding.
Indications for prescribing analysis
The study is a typical method for detecting a malignant tumor of the colon and rectum in the initial stages of development.
A positive test result may indicate the development of colorectal cancer The doctor prescribes the donation of biomaterial if certain symptoms are present. which the patient addresses:
- abdominal pain, acid reflux, nausea, vomiting (follow this link to find out);
- systematically repeated false urge to defecate;
- regular constipation or diarrhea, fever, chills, lack of appetite, rapid weight loss;
- after detection of tumors in the gastrointestinal tract, diagnosis is necessary to exclude internal bleeding;
- helminths - a study is carried out to determine the degree of damage to the inner lining of the gastrointestinal tract (from this publication you will learn);
- previously discovered ulcers, Crohn's disease, infectious diseases caused by Mycobacterium tuberculosis.
Testing every 2 years is prescribed during preventive examinations after 50 years for timely diagnosis of colorectal cancer. Indications for the test pose a health risk. If your doctor recommends a stool test, you should not take it lightly. The process of taking a stool occult blood test is absolutely safe and painless. The diagnostic price varies from 300 to 750 rubles.
Watch in the next video what the indications may be for prescribing a stool test for occult blood.
Types of occult blood tests
Laboratory testing allows you to find biological fluid in the intestines. The research is carried out in two ways:
1
Benzidine test (Gregersen method)
The method detects the presence of hemoglobin even in a small volume - which is both an advantage and a disadvantage of this type of research. Used to register colorectal bleeding.
2
Immunochemical method
The fecal occult blood immunochemical test focuses exclusively on a person's hemoglobin, so there is no need to follow a diet that excludes foods rich in iron-containing protein before the test.
The method is not able to detect colorectal bleeding in the stomach, esophagus and duodenum.
The immunochemical type is more reliable, it will detect 0.05 mg of iron-containing protein in 1 g of sample (with 0.2 biomaterial the test is positive). The choice of type of testing is made by the doctor and depends on the reason for issuing the referral for testing.
Preparing for analysis
To take the benzidine test, you should stop taking certain medications, in particular aspirin, for 3 days The test result will be accurate if you follow the rules for preparing for the test. They are different for each method (in this publication you will read how to prepare for the test).
Preparation for a stool occult blood test using the Gregersen reaction:
- Within 3 days before submitting the biomaterial, stop eating meat, liver and other foods that contain iron (chickpeas, lentils, cashews, apples, dark chocolate, etc.).
- For 3 days, do not take medications that contain iron, ascorbic acid, aspirin and non-hormonal drugs that have an anti-inflammatory effect. Discontinuation of medications should be discussed with your doctor.
- Women are prohibited from donating feces for diagnostics during menstruation, 3 days before and after.
How to take a stool occult blood test, which is performed using an immunochemical method:
- There is no need to adhere to a special diet before testing stool for occult blood..
- If you regularly take medications that increase the risk of bleeding, it is important to consult your doctor about the procedure for conducting the test.
- The test is prohibited from being taken within 14 days after undergoing instrumental methods for diagnosing the digestive tract, which can lead to a violation of the anatomical integrity of the mucous membrane (these include colonoscopy, sigmoidoscopy and others).
Compliance with the rules is the key to obtaining a reliable result of the study of biomaterial.
How to properly collect feces
The material is collected from the vessel into a universal container using a special spatula attached to the lid of the container The collection is carried out after spontaneous defecation (taking biomaterial after using an enema or laxatives is not allowed!).
The material is collected in a universal transport container. You can buy a container at pharmacies and laboratories.
The required sample volume is tsp. from 3 servings. It is forbidden to take areas contaminated with urine and discharge from the genitals. Material containing blood is not examined.
You can't take material out of the toilet. To do this, use a duck or a special vessel. In newborn babies, feces are collected from a cotton diaper immediately after defecation.
How to get tested
Having received a referral for a test, the patient independently decides where to go for the test: to a public medical institution or to a private laboratory.
Rules for storing and transporting feces: up to 12 hours at a temperature of 4-8 °C. The biomaterial must be delivered to the laboratory on the day of collection.
How much stool occult blood testing is done depends on the method chosen. The study using the immunochemical method takes about 14 days, and the Gregersen reaction - 4 days.
There is a test for rapid research using the immunochromatographic method. To implement this, a tablet has been developed that reacts to human hemoglobin cells in feces.
How to conduct express research yourself:
- buy a rapid diagnostic test at a pharmacy;
- open the package;
- collect feces with an applicator into a container with a reagent;
- Add 2 drops of liquid to the tablet with an indicator;
- wait for the results to appear.
The appearance of two stripes means that the diagnosis of the biomaterial for colorectal bleeding is positive; you should consult a doctor for further clarification of the circumstances. Correct use of the rapid test allows you to obtain a result with a reliability level of 99.9%.
Read in this article how to decipher a urine test for protein levels.
How to determine the presence of blood in stool
There are two types of stool occult blood tests: the immunochemical method and the benzidine test. The Gregersen reaction is carried out as follows: 0.025 g of basic benzidine and 0.1 g of barium compound with oxygen are mixed, and 5 ml of 50% ethanoic acid is added before the test. The reagent is shaken until a homogeneous solution is obtained.
A thin layer of biomaterial is applied to the cover glass with a smear, then a few drops of the prepared reagent are added on top.
The color of the biomaterial in blue or green indicates the presence of biological fluid. This is due to the fact that when interacting with benzidine, the hemoglobin molecule is oxidized by hydrogen peroxide and changes color.
Analysis of feces for occult blood by the immunochemical method is based on the antigen-antibody adhesion reaction between the human iron-containing protein and anti-HbF antibodies present in the sample on latex microspheres. The adhesion and precipitation from a homogeneous suspension of antigen-bearing cells under the influence of specific substances is measured as an increase in absorbance of 570 nm, the size of which is directly dependent on the level of hemoglobin in the sample.
Decoding the results
Normally, the human body excretes blood with feces in the amount of 2 mg or less of iron-containing protein per 1 g of material. A positive result indicates the presence of internal blood in the biomaterial. The intensity of the reaction is marked with a “+” sign: weakly positive (“+”), positive (“++” or “+++”) and strongly positive (“++++”).
In a healthy person, the benzidine test result should be negative In a healthy person, the result of a benzidine test test is negative. A negative indicator is not significant for establishing a diagnosis.
Positive means that the stool contains biological fluid in an amount greater than normal.
This is a sign of the presence of diseases such as: stomach ulcer, inflammation of the duodenum, ulcerative colitis, malignant tumor of the stomach, thrombophlebitis, varicose veins of the esophagus, stomatitis, periodontal disease, periodontitis, bleeding from the gums or nasopharynx.
If the result is positive, it is necessary to retest, since there is a possibility of an incorrect result due to deviation from the instructions for obtaining the biomaterial.
The standard result for stool occult blood analysis using the immunochemical method: 0-50 ng/ml.
A positive stool occult blood test indicates bleeding in the digestive tract. Based on the test results, it is impossible to judge in which part of the digestive tract it occurs and what the reason for this is. To obtain additional data, endoscopic diagnostics (sigmoidoscopy, colonoscopy) are required.
If a negative result is obtained, the presence of colorectal cancer cannot be completely ruled out. Only a specialist should interpret the stool occult blood test.
Causes of false positive and false negative results
In some cases, the result of a stool occult blood test is false positive. The reason for this may be poor preparation for collecting material. A false positive test may be due to bleeding from the gums and nose, causing the person to swallow a small amount of blood.
A false positive result may be the result of menstrual fluid in the stool, as well as adherence to a meat and fish diet.
False-negative indicators can occur if there is no free hemoglobin in the feces, but only undestroyed fresh red blood cells as a result of external bleeding (for example, from an anal fissure).
Taking stool samples 2-3 times is more informative. This will eliminate false positive and false negative indicators. If the repeated test shows the original result, then it is reliable.
conclusions
A diagnosis cannot be made based on what a stool occult blood test shows. A positive result means that the disease is progressing and, in combination with the signs and symptoms exhibited, allows a preliminary diagnosis to be made.
– laboratory examination of stool aimed at identifying hemoglobin. The fecal hemoglobin test is performed as a screening for minor internal bleeding. Determination of occult blood in feces is used to diagnose pathological processes in the gastrointestinal tract, with varicose veins of the esophagus, 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. In total, 449 addresses were found in Moscow where this analysis could be done.
– laboratory examination of stool aimed at identifying hemoglobin. The fecal hemoglobin test is performed as a screening for minor internal bleeding. Determination of occult blood in feces is used to diagnose pathological processes in the gastrointestinal tract, with varicose veins of the esophagus, 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 a patient has severe 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 (preferably once every 2 years for patients of pre-retirement age), if a tumor is suspected, as well as for people suffering from helminthiasis, polyposis, gastric erosion or ulcerative colitis. If a neoplasm of the gastrointestinal tract (benign or malignant) is diagnosed using an instrumental method, then the patient is advised to test stool for occult blood to exclude minor bleeding. Symptoms for which a study is prescribed 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 manifests itself as clinical symptoms of hypochromic or microcytic anemia, therefore, if there are signs of anemia, not only an instrumental examination (gastroscopy and colonoscopy) should be performed, but also a stool test for occult blood.
Preparing for analysis
Collection of stool for analysis of occult blood is carried out in the morning (in women no earlier than the 7th day of the 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 +8 0 C) 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 gastrointestinal mucosa and the development of minor bleeding in patients due to injuries to the nasal mucosa,