Guaiac test

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The guaiac -based stool blood test (also known as guaiac-based fecal occult blood testing or FOBT ), briefly guaiac test (modified method according to Greegor; product names are e.g. Haemoccult, HEMDETECT, hemo CARE or hemo FEC) is used for the biochemical detection of Blood (occult) in stool that is not visible to the naked eye ( macroscopically ) . This can occur with colorectal cancer . The test is therefore used to screen for this disease.

Test principle and implementation

Two small stool samples from each of three consecutive stool movements are spread on filter paper impregnated with guaiac resin and then dripped with hydrogen peroxide solution. If blood is present in the stool, the test strip turns blue due to the pseudoperoxidase effect of the heme residue in the hemoglobin : With the help of peroxidase, the hydrogen peroxide oxidizes guaiaconic acid in the guaiac resin to guaiac blue . The test is considered positive if at least one of the test fields shows a blue color after development.

Evaluation and alternatives

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

False-positive results can be caused by eating raw meat ( myoglobin ) or vegetables containing peroxidase (e.g. cauliflower, radish, tomatoes, broccoli), by microbleeding in the upper gastrointestinal tract when taking ASA or other NSAIDs , as well as by gum, Nasal, hemorrhoidal bleeding occur. False-negative results can be caused by oral administration of vitamin C ( ascorbic acid ) or the consumption of fruit rich in vitamin C.

Taking iron supplements has no effect on the result in today's tests. The black coloration of the stool caused by this can, however, simulate gastrointestinal bleeding (in the sense of tarry stool ).

Alternative methods are the haematoporphyrin test and immunochemical tests , which have sensitivities of 60 to 90% and are quite specific . Colonoscopy , in which over 95% of tumors are detected, is the gold standard of bowel tumor diagnosis . Since these procedures are more expensive and sometimes more invasive and complex (colonoscopy), stool tests based on the guaiac principle continue to play an important role in the early detection of colon cancer.

The Federal Joint Committee (G-BA) decided in April 2016 that new test procedures will be used in the future for the early detection of colon cancer. Quantitative immunological tests for the detection of invisible blood in stool ( iFOBT ) are replacing the guaiac-based test (gFOBT) currently in use. The iFOBT is said to reveal a disease with a 5% higher probability.

Individual evidence

  1. ↑ David H. Greegor, Jr .: Occult blood testing for detection of asymptomatic colon cancer . In: Cancer . tape 28 , no. 1 , 1971, p. 131-134 , doi : 10.1002 / 1097-0142 (197107) 28: 1 <131 :: AID-CNCR2820280125> 3.0.CO; 2-I , PMID 5110619 .
  2. ↑ a b c R.M. McLoughlin, CA O'Morain: Colorectal cancer screening. In: World journal of gastroenterology. Volume 12, number 42, November 2006, pp. 6747-6750, doi : 10.3748 / wjg.v12.i42.6747 (currently unavailable) . PMID 17106920 , PMC 4087426 (free full text) (review).
  3. ↑ Hemoccult ® SENSA ® test - Beckman Coulter GmbH. Preparation information. In: Yellow List Pharmindex . Medical Media , February 15, 2014, accessed March 1, 2014 .
  4. ↑ James E. Allison, Irene S. Tekawa, Laura J. Ransom, Alyn L. Adrain: A Comparison of Fecal Occult-Blood Tests for Colorectal-Cancer Screening . In: The New England Journal of Medicine . tape 334 , no. 3 , 1996, p. 155-159 , doi : 10.1056 / NEJM199601183340304 , PMID 8531970 .
  5. ↑ David A. Lieberman, David G. Weiss et al. a. (Veterans Affairs Cooperative Study Group 380): One-Time Screening for Colorectal Cancer with Combined Fecal Occult-Blood Testing and Examination of the Distal Colon . In: The New England Journal of Medicine . tape 345 , no. 8 , 2001, p. 555-560 , doi : 10.1056 / NEJMoa010328 , PMID 11529208 .
  6. ↑ Sidney J. Winawer et al. a .: Colorectal cancer screening . Clinical guidelines and rationale. In: Gastroenterology . tape 112 , no. 2 , 1997, p. 594–642 , doi : 10.1053 / gast.1997.v112.agast970594 , PMID 9322544 ( elsevierhealth.com [PDF]).
  7. ↑ Entry on guaiac test in Flexikon , a wiki from DocCheck , accessed on November 26, 2015.
  8. ↑ Colon cancer screening will be based on a new test procedure , PM G-BA dated April 21, 2016, accessed on April 26, 2016
  9. ↑ Graser et al .: Comparison of CT colonography, colonoscopy, sigmoidoscopy and faecal occult blood tests for the detection of advanced adenoma in an average risk population. In: Gut 58 (2), 2009. pp. 241–248 doi: 10.1136 / gut.2008.156448
  10. ↑ "National Cancer Plan" ( Memento from March 6, 2016 in the Internet Archive ) (PDF; 270 kB). Field of action 1: Objectives paper 2 b. Further development of colorectal cancer early detection (including development of organized colorectal cancer screening)