Final answer:
In a Hemoccult test, a positive indication of blood is signified by a blue-green color change on the guaiac paper. This reaction occurs when the heme component of hemoglobin in blood interacts with the test chemicals. The specific color range for a positive result varies according to the test kit instructions.
Step-by-step explanation:
When performing a Hemoccult test, a blue-green color is a positive indicator of blood. This test is a form of fecal occult blood test used primarily to detect blood in the feces, and it’s a useful screening tool for colon cancer. The Hemoccult test uses a guaiac paper that reacts with the heme component of hemoglobin when blood is present, leading to a color change. It's important to note that the color change must be within a specific range described by the test instructions to be considered positive. Moreover, this change indicates only the presence of blood, not specifically human blood, as the test will also react with blood from certain foods like red meats or some raw vegetables.
In contrast, the Sure-Vue test for heterophile antibodies uses horse red blood cells and results in moderate-to-large sized dark clumps against a blue-green background as a sign of a positive test. Other tests, like the complement fixation test and the hemagglutination test, also use red blood cells and color changes to indicate test results; however, their outcomes are judged by different standards. For instance, hemolysis in the complement fixation test will produce a pinkish color, while aggregation of erythrocytes in the hemagglutination test results in a red color throughout the well.