Stool guaiac test

The Guajakbasierte fecal occult blood test (also known as guaiac -based fecal occult blood testing or FOBT ) or short guaiac test ( modified method according to Greegor; product names are eg Haemoccult, hemo CARE or hemo FEC ) is used for biochemical detection by the naked eye (macroscopic ) not visible ( occult ) blood in the stool. This may occur in a colorectal carcinoma, therefore the test is the screening of this disease.

Test principle and implementation

Two small stool samples from three consecutive bowel movements are painted on impregnated with guaiac filter papers and then sprinkled with hydrogen peroxide solution. In the presence of blood in the stool there is a blue coloration of the test strip due to the Pseudoperoxidasewirkung of the heme moiety in hemoglobin: Using the peroxidase, the hydrogen peroxide guaiaconic acid oxidized guaiac to Guajakblau. The test is considered positive if at least one of the test fields after development shows a blue color.

Review and alternatives

The sensitivity (sensitivity ) of the test for colon cancer is only about 20 to 40% and is even lower for adenomas as precursor. Nevertheless, can be discovered by repeated tests at regular intervals 90 % of the tumors and reduce mortality from colorectal cancer ( colorectal cancer ) by about 20%. A positive test is followed by a colonoscopy ( colonoscopy ) for clarification.

False-positive results can occur from eating raw meat ( myoglobin) or peroxidase -containing vegetables (eg cauliflower, radish, tomatoes, broccoli), by micro upper gastrointestinal bleeding while taking aspirin or other NSAIDs, as well as through the gums, nose, hemorrhoidal bleeding occur. False negative results might be caused by oral administration of vitamin C (ascorbic acid ) or to the consumption of vitamin C -rich fruit.

The intake of iron supplements does not affect the result in the present tests. However, The consequent blackening of the stool may mimic gastrointestinal bleeding ( within the meaning of tarry stool ).

Alternative procedures are hematoporphyrin test and immunochemical tests, the sensitivity of 60 to 90 % and being quite specific. Gold standard of diagnosis of tumors of the colon is colonoscopy detected in over 95 % of the tumors. Since these methods are more expensive and sometimes invasive and expensive ( colonoscopy ), the stool tests continue to play an important role in colon cancer screening by the Gujak principle.