Fecal Occult Blood Test: Causes In Adults, Which Shows

2024 Author: Rachel Wainwright | [email protected]. Last modified: 2023-12-15 07:39

Analysis of feces for occult blood: methods, preparation rules, interpretation of results

The content of the article:

Causes of gastrointestinal bleeding
Benzidine test
Immunochemical analysis of feces for occult blood
Rules for collecting material for analysis for occult blood
Decoding the analysis of feces for occult blood

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

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

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

Causes of gastrointestinal bleeding

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

peptic ulcer of the stomach and duodenum;
polyps, benign and malignant tumors of the gastrointestinal tract;
nonspecific ulcerative colitis;
Crohn's disease;
diffuse familial polyposis;
hemorrhoids;
anal fissures.

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

A special disposable container for collecting feces for the determination of occult blood in it can be purchased at the pharmacy

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

Benzidine test

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

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

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

Diet in preparation for the study:

dairy products (fermented baked milk, kefir, cheese, feta cheese, cottage cheese, milk);
porridge (oatmeal, rice, millet);
vegetables (potatoes, carrots, cabbage);
fruit;
weak tea, still mineral water;
sweets and confectionery.

Immunochemical analysis of feces for occult blood

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

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

Rules for collecting material for analysis for occult blood

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

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

The day before taking a fecal occult blood test, the patient is not recommended to brush his teeth, since a brush, especially with a stiff bristle, can injure the gums, causing them to bleed.

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

It is necessary to take measures to prevent urine or vaginal discharge from getting into the material; for this, you should urinate before defecation, and then wash and dry the perineum with a towel. During bowel movements, do not straining too much.

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

Decoding the analysis of feces for occult blood

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

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

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

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

The cause of latent bleeding can be a disease of any part of the digestive tract, leading to damage to the mucous membrane

If all the rules for the preparation and collection of feces for occult blood were followed, and factors affecting its reliability were excluded, the detection of blood in it indicates the presence of stomach or intestinal diseases in the patient, proceeding with a violation of the integrity of their mucous membrane: