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Decryption of analyzes

Analysis of fecal occult blood: preparation, delivery, interpretation of results

Gastrointestinal bleeding can turn out very tragic, if it is not detected in a timely manner. In the case of pronounced red feces, doctors have no doubts about the presence of internal pathological processes, but some diseases are almost asymptomatic.

And only the smallest particles of blood in the fecal masses are a sign of disorders of the gastrointestinal tract. Conducting such a study requires adherence to a number of rules to eliminate a false result.


Types of analysis of fecal occult blood

Analysis of fecal occult blood:

Damage to the digestive tract can be localized in both the upper and lower sections. If the bleeding has opened in the stomach or duodenum, then the stool becomes dark red, and in the large intestine - bright red.

But not with every disorder appears such a chair. Often, small ulcers and inflammation only sometimes bleed. There are cases of tumor development, the only symptom of which is only a small admixture of hemoglobin in feces.

Laboratory research provides an opportunity to determine the presence of blood in the intestine. Analyzes carried out in two ways:

  1. Gregersen method (benzidine test).
  2. Immunochemical method.

The Gregersen method shows the presence of hemoglobin even very low concentrations. This is both the virtue and the disadvantage of analysis. In the presence of benzodine, the iron of the transport molecule is oxidized under the influence of hydrogen peroxide and becomes blue.

The reaction goes to hemoglobin, both human and extraneous (contained in meat products). Therefore, to clarify the results, doctors often resort to the second method.

Immunochemical analysis of feces more accurate. It is based on the specific effect of antigens on antibodies specific to a particular person. The method is usually used in infectious diseases, but this does not affect the primary purpose of the study, the determination of blood in the feces.

And if it is additionally possible to establish the type of pathogenic microorganisms that provoked inflammation of the intestine, the diagnostic measure can be considered even exceeded. The lack of immunochemical analysis lies in its duration: only after 2 weeks, doctors make a diagnosis.

When is the analysis assigned?

When analysis is assigned

Delivery of feces for occult blood is not appointed just like that. Usually, the patient complains of abdominal pain or malaise. General indications for the test are as follows:

  • recurrent or persistent abdominal pain;
  • regular nausea, vomiting, diarrhea, or heartburn;
  • chronic stool disorder;
  • rapid weight loss for no apparent reason;
  • to confirm the diagnosis (for ulcers, gastritis, etc.).

In fact, the purpose of the analysis is to identify damage to the intestinal walls and stomach. And if the doctor insists on a detailed examination of the feces, the patient should not refuse.

The test is carried out without any internal interventions, so it will not hurt. However, the high sensitivity of the reagents requires special preparation of the patient.

Preparation for the analysis of fecal occult blood

Any research has an error. But to get reliable results, you must follow a diet before the analysis. First of all, it is necessary to refuse meat and fish, because they contain hemoglobin.

Also, the list of restrictions includes iron-containing and all red foods (tomato, beet, etc.), which stains the stool of even a healthy person. Diet is a key point, but doctors call other requirements:

  1. Cancel medication 1 week before analysis.
  2. The ban on laxatives (including folk).
  3. The day before the analysis, you can not brush your teeth (there is a risk of damage to the gums and distortion of the results).
  4. The analysis is taken not earlier than 3 days after x-ray examination.
  5. Enemas are excluded (emptying should be natural).
  6. Women take an analysis on days when there is no menstruation.

How to take feces?

Not every person can observe such a prohibition as “it is impossible to eat”. Preparation for the analysis requires the mandatory implementation of this item, otherwise the result of the study will be very doubtful. But important is the process of taking feces:

  • It is necessary to prepare the container (sold in a pharmacy).
  • Feces are needed without any liquid (water, urine, etc.). To do this, in the toilet is allowed to lay an oilcloth.
  • After emptying a teaspoon take 3 fragments of feces.
  • Samples should be delivered to the laboratory within 3 hours.

Deciphering fecal occult blood test

Deciphering fecal occult blood test A small amount of blood still gets into the intestine - 1-2 ml. This is normal only if such a volume is the daily limit.

Therefore, the analysis will always show the presence of blood in the feces, but can such a small amount be considered a sign of disorder? Not. Natural processes have not been canceled, and doctors take into account only the highest rates.

False Results

To obtain reliable results of the analysis of fecal occult blood, the preparation should not be ignored. And if you treat this process carelessly, the results are often false.

Moreover, both false-negative and false-positive. For example, doctors know for sure that the patient has polyps in the area of ​​the large intestine, but the analysis does not reveal hemoglobin.

This is due to the fact that such neoplasms do not bleed at all constantly, but only periodically. But it would be foolish to deny the presence of polyps, especially if detected with an endoscope.

A false positive result is also a frequent occurrence. If the patient has neglected the rules of preparation and taking feces, then it is quite possible that the study will show the presence of a high level of hemoglobin in the absence of internal bleeding. The analysis is usually carried out according to the method of Gregersen, which is sensitive to iron.

Having eaten only 1 apple a day before taking feces, a person will simply distort the results. In addition, blood can enter the intestine due to a gum trauma with a toothbrush.

Thus, non-compliance with the rules will give doctors a reason to perform a colonoscopy, the essence of which is the introduction of the probe through the anus. So it is better to undergo such an unpleasant procedure not because of your own negligence!

What does a positive result mean?

And yet, the analysis can show the presence of high levels of hemoglobin in the fecal masses. In this case, a colonoscopy is assigned to clarify the diagnosis, because there are many causes of bleeding:

  • ulcer;
  • inflammation in any departments;
  • Crohn's disease;
  • hemorrhoids;
  • helminthiasis ;
  • tuberculosis;
  • bowel crack;
  • a benign or malignant tumor (polyps, cancer, cyst, etc.).

Often, blood enters the intestine from the mouth or nose. However, vascular damage in easily accessible areas of the body is easily determined by the appropriate doctors (dentist and otolaryngologist).


The analysis of fecal occult blood is an important diagnostic tool. Sometimes only hemoglobin impurities indicate a pathological process in the intestine. And if violations are detected in a timely manner, then the treatment will not take long.

Doctors recommend at least once a year to take such an analysis, especially in light of the increasing cases of intestinal diseases.


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