Study of feces for occult blood

People with stomach and bowel problems regularly pass a fecal occult blood test. This test is used to detect asymptomatic bleeding from different parts of the digestive tract.

The study is conducted in a clinical laboratory, it is not considered laborious. It is important in the differential diagnosis of anemia. Physicians are well aware of the rules according to which the collection of feces for occult blood should be organized in order to obtain reliable results. Patients should be familiar with them when they are sent to the laboratory.

Diagnostic methods are constantly being improved. In addition to the practice of benzidine test( Gregersen's reaction), tested for years, an immunochemical analysis appeared and became available. The detection of latent blood in the feces provides essential help to doctors in diagnosing the disease, choosing treatment.

Which blood is considered invisible?

First of all it is necessary to determine the terminology. If the blood is visible on the surface of the stool after the act of defecation, then it does not refer to latent bleeding. Its already visible without any analysis. The cause of this sign in adults is most often the rupture of hemorrhoidal veins, cracks in the rectum.

The test for latent blood in feces has in mind the detection of an inconspicuous stool feces when the presence of blood is not visible not only in the eye, but also is not determined by microscopic examination.

Laboratory techniques can show the presence of gastrointestinal bleeding with a blood loss of less than 50 ml. This is typical for acute stages of the following diseases:

• peptic ulcer disease;
• intestinal polyps;
• tumors;
• nonspecific ulcerative colitis;
• of erosive gastroduodenitis;
• diverticulum of the stomach and intestines.

Malignant neoplasm is one of the causes of occult blood in the feces of

. In differential diagnosis, the physician should consider a possible positive result:

• with bleeding from the nose, gums;
• inflammatory diseases of the tonsils and pharynx,
• varicose veins of the esophagus, caused by cirrhosis of the liver;
• ulcers of the esophagus and erosive esophagitis;
• of Crohn's disease;
• is a tuberculous lesion of the intestine;
• helminths in a child;
• blood diseases.

Assessment of the results of the analysis of feces for occult blood is performed by a physician in conjunction with other studies and clinical manifestations. The methods of detection have their own peculiarities. In the diagnosis you need to consider their intended purpose.

Study of stool with benzidine test

The benzidine test was named after the main reagent in the reaction with feces for occult blood. It is more often used in the Gregersen modification( Gragersen test), which added to barium peroxide( para-diaminodiphenyl by chemical structure) barium peroxide and acetic acid for greater activation of the test solution.

The essence of the reaction: the use of the property of hemoglobin erythrocytes to oxidize benzidine. This method can detect microimpurities of blood( hemoglobin erythrocytes), not only in stool, but also in vomit masses, gastric juice. It is used to examine blood-like blemishes in forensic medicine. The sensitivity of the sample is 1: 100 000. Remember the experiences of Sherlock Holmes( it is worth recalling that Conan Doyle was a doctor).

Important point: a positive result is obtained not only when exposed to hemoglobin, but also when myoglobin reacts to muscle tissue( in meat), certain vitamins and drugs with benzidine. This requires adherence to the preparatory period, restrictions in the diet.

Technique for carrying out the benzidine test

The collected feces are smeared in a small amount on the slide. Several drops of reagent are applied to it. If there is blood, then a blue-green color is obtained.

In liquid stools, the reaction is carried out on filter paper through which the excess fluid is absorbed.

To whom is Gregersen's response given?

The main application is the diagnosis of bleeding from the stomach and intestines:

• when clarifying the nature and cause of anemia;
• hemorrhagic diathesis;
• suspected of cancer and polyposis of the intestine;
• revealing the activity of gastric and duodenal ulcers;
• suspected of ulcerative colitis.

What kind of training is needed?

The possibility of cross-reacting with myoglobin requires preliminary preparation of the patient 3 days before the collection of feces:

• it is necessary to exclude meat and fish products, liver dishes;
• at the same time you can not eat iron-rich vegetables and fruits( apples, spinach, Bulgarian pepper, white beans, green onions, zucchini, tomatoes, cauliflower);
• should stop taking iron preparations, vitamin C, aspirin and containing it for headache, nonsteroidal anti-inflammatory drugs( Diclofenac, Naprofen, Ibuprofen);
• is contraindicated in laxative medications and enemas;
• to avoid the effect of bleeding gums is not recommended to brush your teeth.

If shortly before the direction of the study used such diagnostic methods as sigmoidoscopy, colonoscopy, x-ray of the stomach and intestines, then taking feces for latent blood should be postponed for three days. Girls and women should not take an analysis of feces for hidden blood during menstruation. The lack of preparation leads to false positive results.

In infants, the material for the study is taken from the diaper

Evaluation of the results of the benzidine test

The interpretation of the feces analysis for occult blood and the interpretation of the results is the doctor's business. The reaction is evaluated only qualitatively, the negative result is noted in the conclusion of the laboratory.

How intense the outcome of the sample can be judged by the number of crosses: from one( +) to four( ++++).Sometimes instead of( +) they write "traces".In any case, this means the possibility of asymptomatic bleeding, if the rules for preparing and collecting feces for occult blood are not violated.

How to collect feces for analysis?

Feces for concealed blood analysis should be obtained on the day of the study naturally without enemas and laxatives. People with constipation will have to wait for the chair, having a direction on their hands.
Special sterile containers with a spoon and a tight lid are sold in the pharmacy.

In children, feces are collected from a pot, in infants - from a diaper. An adult would also be right to adjust the act of defecation into a clean pot or vessel, cellophane or a piece of paper.

To deliver the container to the laboratory it is necessary till 10 o'clock in the morning.

For the study, enough quantity of feces with a volume of a teaspoonful. Pick up the biomaterial needs a little from 2-3 different sites. The material for the study should be collected on the same day that the analysis is assigned. It is better not to delay transportation. Allowed a short-term storage in the refrigerator at a temperature not lower than +6 degrees.

Immunochemical method and its advantages

The study of feces for latent blood by the immunochemical method has a number of advantages over the Gregersen reaction:

• sensitivity is much higher;
• is specific only to human hemoglobin, does not react to meat myoglobin, vitamins and medications;
• does not require special dietary training;
• is more suitable for diagnosing bleeding from the lower intestine, because the technique uses a reaction to the protein portion of hemoglobin, and it is actively digested in the upper gastrointestinal tract.

The test is included in the algorithm for examining patients with suspected colorectal cancer( with localization in the colon and rectum).The result of the analysis does not contain information about a specific area of ​​the bleeding digestive system and the causes of bleeding.

You should not treat it like a ready diagnosis. In case of a positive result, the test shows that it is recommended to perform an additional colonoscopy to determine the cause of bleeding. The essence of the method: the use of antibodies to human hemoglobin allows to identify the presence of antigens in the material under study and to give a quantitative characteristic.

When is the immunochemical test shown?

The main indications of the study of the pathology of the lower intestine are the suspicion:

• on the tumor;
• polyps;
• ulcerative colitis;
• Crohn's disease.

The use of the technique in the early diagnosis of colorectal cancer( the most common cause of cancer mortality in the population) helps in the timely conduct of a follow-up examination and improve the prognosis of the course of the disease.

The algorithm of population screening provides for priority immunochemical research with the delivery of stool by all persons over 50 years old, and with hereditary problems from 40 years - threefold. If a positive result is found, the appointment of a colonoscopy.

Technique for carrying out immunochemical research

The technique uses the principle of immunochromatography:

• a drop of the test material is placed in a well of the plate in which a reagent with specific antibodies and a dye is previously applied;
• in the presence of an antigen from the hemoglobin of erythrocytes, a reaction occurs between them;
• a colored complex is formed;
• with liquid the complex passes into the test zone, along the way it is connected additionally with antibodies;
• in the testing area a certain threshold level of hemoglobin concentration is set, its excess in the sample is indicated by pink-violet marking.

The lab technician can conduct several

analyzes at once. How is the interpretation of the results carried out?

The test gives a false-negative response in the absence of a stool sample of free hemoglobin, the presence of only undisturbed erythrocytes, for example, if there is external bleeding from an anal fissure.

The physiological loss of erythrocytes with feces forms a limit for the normal level of the result of -14 ng / ml. Diagnostic thresholds are established depending on the purpose of the study. For example, to detect cancer in the risk group - 50 ng / ml is considered normal concentration of free hemoglobin. Do you need special preparation for analysis?

Unlike the benzidine test, no special dietary restrictions are required. But there are some peculiarities:

• it is necessary to decide with the attending physician the possibility of examining the use of drugs that increase the risk of bleeding( aspirin derivatives, non-steroidal anti-inflammatory drugs);
• analysis is not performed within 14 days after instrumental studies of the stomach and intestines, cleansing enemas, colonoscopy, sigmoidoscopy( they can cause damage to the mucosa);
• is not recommended to take feces from the toilet, it is better to use a sheet of paper, oilcloth, cellophane;
• standard container must be filled in 1/3;
• delivery to the laboratory should be provided within 12 hours after defecation;
• can store the sample in the refrigerator at a temperature of plus 4-8 degrees before transportation.

Feces need to be obtained without enemas and laxatives

Is accelerated express diagnostics possible?

The question of how much analysis is done should be found in the laboratory, where the research material is delivered. In the pharmacy network, you can find a specific test "ImmunoCHROM-GEM-Express."This is an option for immunochemical rapid determination of hemoglobin.

Can be carried out at home. But beforehand, you should carefully read the instructions and fulfill the training requirements. It takes several minutes to get the result of the benzidine test. The patient can receive the conclusion by the end of the working day. The immunochemical test will take 3-6 days.

Conducting a study of feces for occult blood is an important point in the diagnosis of many diseases. The preparation and the rules for taking the analysis should be taken seriously. This will avoid serious complications in the future.