If symptoms occur, the doctor must confirm the diagnosis with objective tests before prescribing treatment. First of all, laboratory tests are carried out, which can show deviations from the norm.
The patient is prescribed a general analysis of blood, stool, and urine. If a specialist suspects that a pathology of the gastrointestinal tract is developing, leading to internal bleeding, then a test is prescribed to detect it.
Why is a test performed to detect occult blood in stool?
With pathology of the mucous membrane of the esophagus, stomach, and duodenum, stool becomes almost black or dark red due to contact of blood with enzymes. If the integrity of the intestines is compromised, the stool becomes bright red. If there is significant bleeding, the patient needs emergency medical attention.
Bleeding is not always constant; ulcers and inflammations bleed periodically. With little involvement of blood vessels in the pathological process, the color of the stool and its consistency do not change.
If no blood is detected during coprogram, and the doctor suspects hidden bleeding, then the patient must undergo another test. The reaction to occult blood in the stool is positive, but bleeding is not necessarily present, that is, the result is false positive.
When is the test taken?
- abdominal pain that is constant or occurs periodically;
- nausea and vomiting;
- heartburn;
- bowel movements differ in consistency from the norm (mushy);
- false urge to defecate;
- frequent constipation;
- diarrhea;
- weight loss, lack of appetite;
- hyperthermia.
If the bleeding is not severe, then it is impossible to notice blood in the stool without special reagents
The study allows you to confirm the diagnosis. It is also carried out if the patient has gastrointestinal diseases using other diagnostic methods. The results will help the specialist understand the extent of damage to the mucosa and determine the severity of the disease, and a repeat test will show how effective the prescribed therapy is.
How to get tested
A therapist, oncologist, surgeon, or gastroenterologist can prescribe the test. Before taking the test, preliminary preparation is required. Doctors give the following recommendations. 72 hours before the test, exclude iron-containing foods from the menu, as well as tomatoes and green vegetables and fruits. You should not eat meat or fish, as they contain hemoglobin.
For a week, stop taking medications such as aspirin, laxatives, iron tablets, non-steroidal anti-inflammatory drugs. If it is not possible to stop drug therapy, then you need to inform your doctor about the medications you are taking.
Do not consume foods that change the color of stool. The collection of material should be carried out before diagnostic manipulations in the digestive tract. It is not recommended to do an enema or take laxatives to speed up the collection of a sample for analysis.
The sample should not be collected during menstruation. If X-ray diagnostics were performed, the analysis can be taken only after 2-3 days.
If the subject has periodontal disease, in which there is severe bleeding of the gums, then the day before collecting stool, it is not recommended to brush your teeth, since blood that gets into the stomach can give a positive result.
You need to take material from three different sides of the stool. An unreliable answer is likely if water or urine gets into the sample. In order to eliminate this, it is recommended to lay oilcloth on the toilet. The test sample must be placed in a plastic container (can be purchased at a pharmacy) and brought to the laboratory within the next 2-3 hours.
What does it mean if the result is positive?
The test for occult blood is positive if a pathology develops in which a certain amount of blood enters the lumen of the stomach or intestines. That is, there is a disease characterized by inflammation of the mucous membrane and its perforation.
In some cases, the tumor manifests itself only by the release of a small volume of blood in the stool
Young children may also see blood in their stool. Quite often this is due to the child’s intolerance to cow’s milk. If the baby is breastfed, then even the mother's consumption of milk, butter, or sour cream can cause bleeding.
If a child has lactose intolerance, then you need to carefully select an artificial formula.
Bleeding in a baby can be caused by dysbacteriosis, amoebiasis, colitis, and dysentery. One of the reasons for the presence of blood in the stool is anal fissures, which arise as a result of the passage of too hard stool. This happens if the child does not drink enough fluids.
Tumors in the colon bleed slightly but constantly from the moment they form. If the bleeding has become profuse, it will also be detected during coprogram. An occult blood test helps detect cancer symptoms early, which increases the chances of a favorable outcome of the disease. A positive test for occult blood will be due to bleeding from the nose or gums or throat.
How to determine the presence of blood in stool
During the study, chemical substances are used that, upon contact with a red blood cell, change color due to oxidation. Gregersen's method allows you to see even small amounts of hemoglobin. Benzidine turns iron blue.
Taking into account the speed of staining and its intensity, a weakly positive (+), positive (++ or +++) and strongly positive (++++) reaction is established. When using benzidine, it is possible to establish blood loss in excess of 15 ml/day, which often gives false positive results.
Immunochemical analysis of stool is considered more accurate. It uses antibodies to human hemoglobin, so there is no need to follow a diet. The test is highly sensitive; it will detect 0.05 mg of hemoglobin per gram of stool (at 0.2 ml/g of stool the test is considered positive).
This method allows you to detect tumor formations in the large intestine, but does not detect bleeding from the esophagus or stomach. In 3% of cases, tests give a positive result in the absence of a tumor in the large intestine.
Causes of false positive and false negative results
Normally, there is no blood in the stool, so if there is no pathology that provokes bleeding in the esophagus, stomach or intestines, the test result will be negative. Under some circumstances, a stool occult blood test may produce a false positive or false negative result.
So, often the study does not detect blood in the case of formation in the large intestine, therefore, to confirm colorectal cancer and polyps, colonoscopy or flexible sigmoidoscopy is used.
A false positive result may be obtained if there was no preparation for the test, if there is bleeding gums, or if the patient frequently experiences nosebleeds. There will be blood in the stool if the mucous membrane is injured, for example, the patient cut the esophagus with a fish bone.
As a rule, the test gives a false positive result if the patient ignored the doctor’s recommendations and did not adhere to the diet
More often, an analysis is carried out specifically for the presence of iron in stool, so even an apple eaten yesterday can stain the sample, which will be interpreted as the presence of blood. To exclude false-positive or false-negative results, it is recommended to carry out the diagnosis three times (samples of three consecutive bowel movements) and follow all recommendations for preparing for the study and collecting material.
If tests twice show a large amount of hemoglobin in the stool, then they are considered reliable.
If the analysis turns out to be uninformative, the doctor prescribes a hardware test - a colonoscopy. It involves examining the surface of the colon using an endoscope inserted through the anus.
Such diagnostics will allow you to see the exact location of the lumen. To determine the condition of the lining of the esophagus or stomach, endoscopy is used, in which a flexible tube is inserted through the mouth. In order to exclude an erroneous result, it is recommended to take the test three times.
If the study gives a negative result, the doctor will not rule out a peptic ulcer or cancer of the digestive system. A diagnosis cannot be made on the basis of a single test for occult blood in the stool; it only means that pathology is present and, together with the clinical manifestations of the disease, allows a preliminary diagnosis to be made.
General analysis (coprogram)- 2 days before collecting biomaterial, discard tomatoes, tomato juice, pasta, beets, blueberries, pomegranates and other vegetables and fruits containing dyes.
- For 3 days, stop taking antibiotics, laxatives, and drugs that cause changes in intestinal motor function. Do not use rectal suppositories, ointments, or oils.
- Do not eat exotic fruits, vegetables and foods that are not typical for your diet as a whole. Do not overeat, exclude fatty, spicy, pickled foods.
- If you are taking medications containing iron and bismuth, they must be discontinued 2 days before stool collection.
Attention. After radiography with a contrast agent (barium), collect feces for coprogram no earlier than 7–10 days after the examination. Women are not recommended to take the test during menstruation.
Procedure for collecting stool:
Collect stool for examination in the morning, on an empty stomach. If this is difficult, you can prepare the sample in advance, but no more than 8 hours before submitting it to the laboratory. In this case, store the sample in the refrigerator (do not freeze!).
- Deliver the sample to the laboratory on the day of collection. Before delivering the sample to the laboratory, the container with stool should be kept in the refrigerator at 2–4 °C. Storage at 2-8 °C is allowed - up to 72 hours.
Dysbacteriosis, intestinal group
To obtain the correct result, material for research is taken before the start of antibacterial therapy or in the intervals between courses of treatment, but not earlier than 2 weeks after its completion.
Attention Do not collect feces from diapers. For infants, collect material from a sterile diaper or pre-ironed onesies. If liquid feces are collected, it can be collected by placing an oilcloth under the baby.
Collection rules
- Carry out hygiene procedures and first urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement.
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine and pieces of undigested food.
The sample can be stored for no more than 2 hours at room temperature; no more than 6 hours at 2-8 °C, more than 6 hours - frozen.
Protozoa and helminth eggs
To obtain the most reliable results, three stool examinations are recommended with an interval of 3–7 days.
Attention You cannot collect stool earlier than 3 days after an enema, an X-ray examination of the stomach and intestines, or a colonoscopy. The day before, do not take laxatives and drugs that affect intestinal motility (belladonna, pilocarpine), activated carbon, iron, copper, bismuth, barium sulfate, use fat-based rectal suppositories. Women should not collect stool during menstruation.
Collection rules
- Feces should be collected in the morning, on an empty stomach. If this is difficult, you can prepare the sample in advance, but no more than 8 hours before submitting it to the laboratory. In this case, the sample should be stored in the refrigerator (do not freeze!).
- Carry out hygiene procedures and first urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement.
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine, water and pieces of undigested food;
- Deliver to the laboratory on the day of collection.
Bacteriology
To obtain a reliable result, material for research is taken before the start of antibacterial therapy or in the intervals between courses of treatment, but not earlier than 2 weeks after its completion.
- 3-4 days before the study, it is necessary to stop taking laxatives, castor and petroleum jelly and stop administering rectal suppositories.
Attention: Feces obtained after an enema, as well as after taking barium (during an X-ray examination), are not suitable for research.
Collection rules
- Feces should be collected in the morning, on an empty stomach.
- Carry out hygiene procedures and first urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement.
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine and pieces of undigested food.
- Deliver to the laboratory on the day of collection.
PCR studies
Collection rules
- Feces should be collected in the morning, on an empty stomach.
- Carry out hygiene procedures and first urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement.
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine and pieces of undigested food.
- Deliver to the laboratory on the day of collection.
Culture for microflora and sensitivity to antibiotics
3-4 days before the study, it is necessary to stop taking laxatives, castor and vaseline oil, and stop administering rectal suppositories. Feces obtained after an enema, as well as after taking barium (during X-ray examination) are not accepted for examination!
Attention: Feces are collected before starting treatment with antibacterial and chemotherapy drugs.
Collection rules
- First urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement.
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine and pieces of undigested food.
- Deliver to the laboratory on the day of collection. If it is impossible to quickly deliver the sample to the laboratory, you can store it in the refrigerator for no more than 4 hours at 2-8 °C.
For carbohydrates
- Carry out hygiene procedures and first urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement.
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine and pieces of undigested food.
- Deliver the sample to the laboratory within 4 hours.
Attention Storing a stool sample for more than 4 hours, including in the refrigerator, is not allowed.
For hidden blood
- Nutrition. For 3 days before stool collection, exclude:
Products containing iron (apples, bell peppers, spinach, white beans, green onions, etc.);
Products containing iodine, bromine (almonds, peanuts, beans, table salt, sour cream, etc.);
Meat and meat products;
Fish and fish products;
All green vegetables and fruits;
All red vegetables;
Products that injure the oral mucosa (caramel, nuts, dried fruits, crackers).
- Drugs. Avoid taking medications, as well as aspirin, indomethacin, phenylbutazone, coroticosteroids, and iron-containing reserpine.
- Alcohol. Exclude 3 days before the study.
Attention. To obtain reliable results, you should not donate stool during bleeding (hemorrhoids, constipation, oral diseases, menstruation). On the day of stool collection, do not brush your teeth, so as not to injure the oral mucosa; you can rinse your mouth with a soda solution. To analyze stool in children, it is allowed to take it from a diaper, diaper, or potty.
Collection procedure
- Feces are collected in the morning, on an empty stomach, after spontaneous bowel movements.
- Carry out hygiene procedures and first urinate in the toilet and flush.
- Place sterile paper (or an ironed sheet) or a disposable plastic plate in the bowl or bottom of the toilet and perform a bowel movement. Collecting stool samples from the toilet is not allowed!
- Collect feces immediately after defecation from different places in a single portion with a special spoon mounted in the lid of a plastic container in a volume of 1–2 g (no more than 1/3 of the container’s volume). Avoid contact with urine and pieces of undigested food.
- Deliver the sample to the laboratory on the day of collection.
Content
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:
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Benzidine test |
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required:
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Immunochemical test |
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Guaiac test |
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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:
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Time to study |
What to do |
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affect intestinal motility |
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stop taking:
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change the color of stool |
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don't have anal sex |
possible damage to mucous membranes |
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remove from diet:
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include iron, pigments |
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exclude fish, meat, offal (for guaiac or benzidine testing) |
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Deadline for performing a stool test:
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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 stool 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 or dangerous diagnoses in the body, 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 the following cases:
- lack of preparation for the study;
- presence of nosebleeds;
- violation of the recommended diet;
- use of medications;
- bleeding gums.
The cause of a false negative result may be a violation of the analysis technology or low-quality reagents. If there is a suspicion of the development of pathologies, a repeat examination is required. A false negative result occurs in the following situations:
- limited amount of biomaterial provided for testing;
- uneven distribution of blood particles in the stool;
- the presence of tumors, polyps that bleed occasionally.
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Normally, blood should not be found in the stool, but there are pathological conditions in which such a phenomenon is considered one of the characteristic signs.
Hidden blood is a specific condition in which bloody masses in the stool are not visible to the naked eye, even under a microscope, however, with a deeper study of the biomaterial, the presence of blood is revealed.
Types of stool tests for occult blood
A variety of tests and screenings are used to detect blood in stool. Today, laboratories use the 2 most informative methods to detect occult blood:
- Immunochemical test. Such diagnostics are usually prescribed to identify pathological processes in the lower parts of the digestive system. The reaction occurs only in the presence of human hemoglobin, so it makes no sense for patients to adhere to any dietary restrictions, for example, to refuse to eat meat and iron-rich foods before diagnosis. Such a diagnosis is more convenient and is usually used as a screening procedure for the subject.
- Gregersen reaction or benzidine test. This test is performed chemically and is used to detect bleeding in all structures of the gastrointestinal tract. Such testing is sensitive not only to human hemoglobin, but also to animal sources of iron, so a strict diet that excludes the consumption of meat products is necessary before diagnosis.
An immunochemical test for occult blood is considered the most informative; however, it is not able to detect bleeding when it is localized in the stomach or esophagus.
Only a specialist decides which research method is most appropriate in the case of a particular patient, so you need to contact a doctor with this question, and only then go to the laboratory to take a sample.
Indications
Typically, the need for analysis arises when there are suspicious symptoms such as:
- Painful syndrome in the abdominal area;
- Frequent diarrhea and constantly liquefied stool;
- Dyspeptic symptoms such as nausea, bloating or heartburn, disturbing for a long time;
- Various digestive disorders;
- Sudden causeless weight loss;
- Clinical examination of stool does not show bleeding.
In addition, test screening for occult blood is carried out in case of suspicion of the presence of colorectal oncology, anemia of unknown etiology, to detect intestinal bleeding and for preventive purposes in patients over 50.
If they are visible without any instruments or research, then this indicates their abundance. An experienced gastroenterologist can determine by the shade of stool where the bleeding focus is located.
If there are bright spots of blood in the stool, this indicates damage to the rectum or large intestine. If the stool has a black tint, the causes of bleeding should be looked for in the stomach or tissues of the esophagus.
Preparation
For maximum reliability of the test for occult blood, it is necessary to properly prepare for the diagnosis.
The main requirement for patients undergoing testing for the Gregersen reaction is to follow dietary recommendations.
Why do you need to exclude fish and meat dishes, seafood, alcohol, vitamin supplements and taking medications containing iron, which have an analgesic and anti-inflammatory effect, several days before the study?
In the latter case, the ban is due to the presence of ibuprofen or aspirin in these drugs. Also, the purpose of the diet is to normalize stool so that it becomes natural without the use of any drugs that may distort the result.
Ladies during menstruation should approach such a study with special care, because if menstrual fluid penetrates into the feces, the reaction will show an incorrect result.
About a week before the study, you should stop using rectal suppositories, oil compresses or microenemas.
You need to be especially careful when brushing your teeth so as not to damage the gums, otherwise blood may penetrate the gastrointestinal tract and appear in the samples during the study, which will lead to an erroneous result.
How to assemble?
The collection of biomaterial is also important for reliability. The feces intended for analysis should not contain any foreign impurities such as urine, water, secretions, etc.
Therefore, it is better to purchase a sterile container from a pharmacy for feces. The potty or vessel will also need to be disinfected. You cannot collect feces from the toilet.
Only natural stool without enemas or laxatives is suitable for the laboratory sample. Urine should not get into the container with feces.
Using a special spoon, you need to transfer the biomaterial into a container. By volume, feces should occupy at least 1/3 of the container. It is better to put several different fractions of feces, then the result will be more accurate.
How to submit?
After collecting stool, you need to send it to the laboratory as soon as possible; the maximum possible storage time is 3 hours.
There is no need to preserve or freeze stool; such samples are not suitable for diagnosis.
If stool has been collected, but it is not possible to deliver it to the laboratory right now, then you can place it in a refrigerator. But storing the sample for more than 3 hours is unacceptable.
What does the study show?
Therefore, any method for detecting rectal blood will show its presence. This is a consequence of natural processes, so doctors do not react to such indicators, paying attention only to higher indicators.
The intensity of the reaction is shown by the number of plus signs. If the result is weakly positive, then the analysis is assessed with one plus sign - “+”, a strongly positive result looks like “++++”.
Negative test results are the norm, but such data do not always indicate the absence of hidden internal bleeding. Sometimes bleeding is periodic, so it is not always detected during test screening.
When is the result positive?
If the result is positive, the doctor concludes that there is much more blood in the stool than is allowed naturally. And this may indicate the development of pathologies such as:
- Infectious processes provoked by Koch's bacillus;
- Inflammatory lesions of the duodenum or;
- Tuberculosis;
- Periodontal disease or stomatitis, gum bleeding or periodontitis;
- Ulcerative colitis;
- Cracks in the intestine;
- Acute inflammation of hemorrhoids;
- Varicose veins or thrombophlebitis of the esophagus;
- Nasopharyngeal bleeding.
Also, hidden fecal blood can be a consequence of nasopharyngeal or throat pathologies. Gum bleeding, vasodilatation in the nose and resulting bleeding can all lead to rectal occult blood.
If a patient has a positive reaction to fecal blood, then he is usually prescribed a second diagnosis, because no one has canceled the false results. After all, not all patients approach preparation responsibly, violating the doctor’s recommendations.
How long does the examination take?
Results in the laboratory are prepared within several days, usually 3-6 days. The exact time of diagnosis depends on the specific laboratory.
Price
The average cost of diagnostics for occult rectal blood is about 240-900 rubles, which depends on the specific technique and laboratory.
For convenience, today pharmacies have home tests that operate on the immunochromatographic principle and react to human hemoglobin in stool.
The cost of such a test system is about 250 rubles, and the reliability is more than 99%.
Fecal hemoglobin analysis is a very common diagnostic test that allows early detection of dangerous pathological conditions, including oncology. As a result, the patient receives timely treatment, which maximizes the chances of a final recovery.
Video about fecal occult blood testing:
Up to 40-50 years of age, a preventive test for occult blood is taken only based on the results of alarming results of other tests, as well as in the presence of certain symptoms and unfavorable heredity.
The reasons for urgent analysis are:
- undifferentiated pain in the abdominal area;
- iron taste in the mouth;
- heartburn;
- decreased appetite;
- causeless increase in temperature;
- constant nausea with periodic bouts of vomiting in the absence of obvious signs of gastrointestinal diseases;
- unexplained changes in stool of various types (too liquid or too dense, with foamy or mucous inclusions);
- unexpected weight loss.
On a note! A regular test for occult blood in stool is recommended for people over 50 and anyone who suspects Lynch syndrome - a hereditary predisposition of the patient to cancer processes in the large intestine. Calculated based on family history (presence of colorectal cancer in at least 3 blood relatives in 2 generations).
Types of occult blood tests
The test has several varieties:
- guaiac test (Weber-Van Deen reaction);
- benzidine test (as modified by Gregersen);
- immunochemical (immunochromatographic) test.
On a note! Fluorescent analysis is worth mentioning separately. In this case, traces of hemoglobin molecules are detected through its breakdown products - porphyrins, which have a high light absorption coefficient and exhibit a fluorescent glow. However, in the CIS countries this method is practically not used.
Guaiac and benzidine tests
Guaiac test- the oldest method of examining feces for occult blood, first used in 1864 by Van Deen. The essence is to color heme peroxidases (hemoglobin compounds oxidized by hydrogen peroxide) with an alcoholic solution of guaiac resin blue. Other peroxidases also exhibit similar staining, including those found in red meat and some fruits and vegetables, so it is impossible to obtain an accurate result without following a strict diet. But the main “minus” lies in the low sensitivity of the guaiac analysis: the reaction is visually noticeable only with blood loss of 30 ml. In this situation, the percentage of successful detection of gastrointestinal cancer is no more than 15-30%.
Benzidine test- an improved version of chemical analysis. The principle of operation is similar to the guaiac test, but the reagent is a solution of benzidine in acetic acid with an admixture of hydrogen peroxide (or barium - modification according to Gregersen). In the presence of blood, the sample turns blue or blue-green. Similar to the guaiac test, the benzidine test gives positive staining for the pigments of meat and some fruits and vegetables, but has the advantage of being highly sensitive (1:100,000).
Specifics of preparation for guaiac and benzidine tests
The nonspecificity of the reagents to the type of pigment requires strict preliminary preparation:
- 72 hours before donating the biomaterial, exclude animal hemoglobin from your menu (all types of meat and fish), as well as seafood, red and green fruits/vegetables, buckwheat porridge, seeds/nuts, bran and medications containing iron.
- Avoid any products that can damage the gastrointestinal tract (crackers and dryers, hard unrefined cereals, caramel candies).
- Avoid medications that increase intestinal motility and anti-inflammatory drugs.
- If you tend to have bleeding gums within 2-3 days, stop using your toothbrush or replace the bristles with softer ones.
- The day before collecting biomaterial, avoid enemas, rectal suppositories and laxatives.
- All instrumental and hardware examination methods (colonoscopy, sigmoidoscopy, CT, X-ray) are carried out after the occult blood test or no later than a week before it.
Immunochemical analysis
Based on the interaction reaction of human heme with highly specific antibodies that do not form compounds with animal or plant pigments. The analysis is also called an immunochromatographic test, since it operates on the principle of chromatography: a stool sample is applied in a thin layer to a test strip and exposed to monoclonal antigens in a special apparatus. If there is occult blood in the sample, the control area of the test strip will turn pinkish-purple. The test is highly accurate and virtually eliminates the possibility of error.
On a note! An immunochemical analysis can be carried out independently at home (pharmacies sell special self-diagnosis devices), however, with this approach the reliability of the analysis is lower (multiple confirmation is required).
Preparation for an immunochemical test is less specific than for a benzidine test and does not require a special diet. All other recommendations remain in effect.
Rules for sampling
It is more convenient to collect material early in the morning, before breakfast:
- Wash the perineal area thoroughly with regular unscented soap and warm water.
- For defecation, take a specially prepared separate container - clean and dry. The process of defecation itself should be natural; auxiliary medications and enemas are not allowed.
- Take approximately 2-3 teaspoons of feces from different areas of the stool into a sterile container. It is safest to use a special plastic container (sold at any pharmacy). An alternative is to use a thoroughly washed and dried glass jar with a tight-fitting lid.
- Deliver the collected sample to the laboratory. It is best to do this immediately (within 1-2 hours). If problems with bowel movements do not allow this process to be carried out in the morning, the container can be stored in the refrigerator for 12 hours.
Attention! The results of the analysis cannot be considered reliable if the patient at the time of collection of the biomaterial had dyspepsia, hematuria, periodontal disease, nosebleeds, menstruation, bleeding hemorrhoids (of course, if the disease has already been diagnosed). In these cases, as well as after instrumental examination of the gastrointestinal tract, the test for occult blood will be positive.
Decoding the results of the occult blood test
The results of the analysis are issued according to the “+/-” system, indicating the qualitative and quantitative results of the test.
Digital determination of quantity is impossible, since hidden blood is manifested by the presence of color and the degree of its intensity. The more saturated the color of the benzidine sample and the pink-violet spectrum on the chromatogram of the immunochemical analysis, the higher the level of occult blood in the biomaterial.
A negative reaction to occult blood is normal. A positive answer is indicated in the so-called “points” from “+” to “++++” and indicates the intensity of bleeding.
Deciphering can be done by a general practitioner (general practitioner, pediatrician) or a specialist: oncologist, gastroenterologist, surgeon. The results can only be interpreted taking into account data from other tests, so the test has no independent value. Even a negative indicator does not guarantee the absence of pathologies, so the diagnosis must include a whole range of hardware and laboratory tests.
False results
False results are a consequence of a violation of the analysis technology either on the part of the patient (when collecting material) or on the part of the laboratory.
False negative results are rare. Causes:
- insufficient volume of biomaterial;
- disruption of the technological process;
- low-quality reagents.
False-positive results occur more often and are a consequence of improper preparation for the test.
What does a positive result mean?
The most dangerous reason for the appearance of occult blood is the presence of neoplasms. Intestinal tumors may bleed, but in the early stages this process is insignificant. In addition, when exposed to gastrointestinal enzymes, hemoglobin becomes invisible.
In addition to tumors, the reasons for a positive occult blood test are:
- inflammation of the gastrointestinal tract (ulcers, diverticulitis, gastritis, enteritis, colitis);
- Crohn's disease (autoimmune damage to certain parts of the intestinal wall);
- helminthiases;
- varicose veins of the esophagus;
- intestinal polyposis;
- haemorrhoids;
- cirrhosis of the liver;
- Rendu-Osler disease (hereditary predisposition to the formation of angiomas on the surface of the mucous lining of the gastrointestinal tract).
A positive test is not a reason to panic! Given the high probability of errors, you will need to repeat the test (three times). If the analysis is repeatedly confirmed, additional examinations (colonoscopy, enteroscopy, general and biochemical blood tests) are prescribed in order to determine what exactly caused the pathology.
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