Hidden blood in the feces

Blood cells under the

microscope Normally, if the patient is properly prepared, the latent blood in the stool is not detected. Bleeding from the digestive tract is a problem often encountered by practical doctors. The degree of bleeding varies significantly, and the greatest difficulty is the diagnosis of small chronic bleeding. In most cases, they are caused by gastrointestinal cancers. Tumors of the large intestine begin to bleed on the early( asymptomatic) stages of the disease, as a result of which the blood enters the gut.

Various screening tests are used to diagnose bleeding from the gastrointestinal tract in order to detect asymptomatic course of the disease in outwardly healthy people, which allows achieving a positive result of treatment.

Normally, feces produce 1 ml of blood per day( or 1 mg of Hb per 1 g of feces).As you move through the intestines, the blood is distributed in the feces and decomposes under the action of enzymes( digestive and bacterial).

To detect hidden blood in stool, most clinics use benzidine or guaiac test. Hidden is the blood that does not change the color of the stool and is not detectable macro- and microscopically. The reactions for detecting hidden blood are based on the property of the blood pigment Hb to accelerate the oxidative processes. The easily oxidizable substance( benzidine, guaiac), oxidizing, changes color. The speed of the appearance of coloration and its intensity distinguish between a slightly positive( +), positive( ++ and +++) and a sharply positive( ++++) reaction.

When a fecal occult blood test is administered, special patient preparation is necessary( to avoid false positive results).For 3 days before the study, meat dishes, fruits and vegetables containing a lot of catalase and peroxidase( cucumbers, horseradish, cauliflower), exclude ascorbic acid, iron preparations, acetylsalicylic acids and other non-steroidal anti-inflammatory drugs are excluded from the patient's diet. To detect hidden blood, it is recommended to examine the stool after 3 consecutive defecations, each time taking samples from two different feces. When evaluating the results of an analysis, even one positive result should be considered as a diagnostic test( and in cases where the rules for preparing the patient were not observed).

The diagnostic value of the latent blood test in terms of early diagnosis of colon cancer depends on the amount of bleeding from the tumor. On average, blood loss from tumors of the cecum and ascending colon is 9.3 ml / day( from 2 to 28 ml / day) [Henderson DM, 1997].At localizations distal to hepatic bending of the intestine, blood loss is much less and is 2 ml / day. This difference, possible

but, is due to the large size of tumors of the proximal part of the colon. The blood loss from adenomatous polyp averages 1.3 ml / day, regardless of its location.

The reactions used to detect occult blood in the stool have different sensitivities. The reaction with benzidine allows us to detect only blood loss exceeding 15 ml / day, it gives a lot of false positive results and is practically not used at present. The most common test for the detection of peroxidase activity in clinical practice is a guaiac test. Usually, during this test, the stools are applied to the filter paper, and then the guaiac reagent, acetic acid and hydrogen peroxide are added thereto. In this setting, the method is very sensitive to the detection of peroxidic activity, but it is poorly standardized and often gives false-positive results. In this regard, tests have been developed in which the guaiac reagent is preliminarily deposited on a plastic strip, which allowed the standardization of studies and the diagnosis of even minor bleedings.

The frequency of positive results of a guaiac test depends on the amount of blood in the stool. The test is usually negative with a Hb concentration in the feces of less than 2 mg per gram and becomes positive as the concentration increases. The sensitivity of the guaiac reaction at a concentration of Hb 2 mg per 1 g of stool is 20%, at a concentration of more than 25 mg per gram, 90%.In approximately 50% of cases of colon cancer, the tumor "secretes" enough blood to reveal its guaiac reaction, the sensitivity of which with colorectal cancer reaches 20-30%.The guaiac test also helps in the diagnosis of colon polyps, but the loss from polyps is much less, so the test for the diagnosis of this pathology is not sensitive enough( positive about 13% of cases) [Wallach J. M. D., 1996].Polyps of the distal part of the large intestine( descending part of the colon, sigmoid and rectum) give positive results in 54% of cases, proximal - in 17%.

The quantitative test "Hemokvant"( based on the fluorescent detection of porphyrins in feces) has twice the sensitivity as compared with the guaiac reaction, but it can be influenced by eating meat and taking acetylsalicylic acid for 4 days before the analysis. Normally the content of porphyrins in stool is less than 2 mg / g of feces;2-4 mg / g - border zone;higher than 4 mg / g - pathology.

Given all these shortcomings of traditional screening tests, in recent years a completely new method for diagnosing bleeding from the gastrointestinal tract for the early diagnosis of colon cancer has been developed. We are talking about immunochemical tests( for example, sets "Hemoselect"), which use specific AT to Hb human. They can detect only human Hb in feces, therefore, when using them, there is no need for restrictions in nutrition and drug intake. The tests have a high sensitivity - they even show 0.05 mg of Hb per 1 g of stool( usually values ​​above 0.2 mg / g of feces are considered a positive test result).They do not reveal bleeding from the upper sections of the digestive tract, which allows them to be used purposefully for the diagnosis of tumor lesions of the large intestine. Immunochemical tests are positive in 97% of cases of colon cancer

in a single study and 60% in adeno-matic polyps larger than 1 cm. In 3% of cases, tests can be positive in the absence of a tumor in the large intestine.

Experience with the use of immunochemical tests by foreign clinics shows that occult blood feces study allows detecting colon cancer at early stages of development and leads to a 25-33% reduction in mortality. In addition, this test is an alternative to the endoscopic( colonoscopy) method for screening colon cancer. Regular screening of feces for latent blood leads to a reduction in the incidence of colon cancer at the late stage of development by 50% [Henderson DM, 1997].

A positive reaction of feces to occult blood is possible with many diseases:

?peptic ulcer of the stomach and duodenum;

?primary and metastatic tumors of the esophagus, stomach, intestines, duodenal papilla;

?intestinal tuberculosis, nonspecific ulcerative colitis;

?invasions of helminths, traumatizing the wall of the intestine;

?expansion of the esophagus in cases of cirrhosis of the liver and thrombophlebitis of the spleen vein;

?Rundu-Osler disease in the localization of bleeding telangiectasis in any place of the mucosa of the digestive tract;

?typhoid fever( in patients with typhoid fever with positive results of reaction to latent blood in stool, macroscopic bleeding occurs much more often than with negative ones, although pronounced bleeding is possible without previous latent ones);

?getting into the digestive tract of blood from the oral cavity and larynx, with lip cracks, with an accidental or deliberate( for the purpose of simulation) sucking blood from the oral cavity and flowing it in cases of nasal bleeding;

?getting into the feces of blood from the hemorrhoids and fissures of the anus;

?getting into the stool of menstrual blood.