Stool guaiac test
（重定向自Hemoccult）
![](/Images/godic/202501/17/Guaiac010557.jpg")
![Both square test areas in the upper area of the card show the intense blue color of a positive result. The lower two smaller circular areas on the orange stripe are analytical control reactions, positive on the left and negative on the right, that help assure that the card and developer bottle have been maintained in proper conditions and have not been damaged before the test is performed.](/Images/godic/202501/17/Guaiac_test0557.jpg")
![](/Images/godic/202501/17/Possible_Guaiacum_blue_formation_reactions.svg0557.png")
The stool guaiac test or guaiac fecal occult blood test (gFOBT) is one of several methods that detects the presence of fecal occult blood (blood invisible in the faeces). The test involves placing a faecal sample on guaiac paper (containing a phenolic compound, alpha-guaiaconic acid, extracted from the wood resin of Guaiacum trees) and applying hydrogen peroxide which, in the presence of blood, yields a blue reaction product within seconds.