digestive disorders
Stool Occult Blood Tests
Guaiac Based Stool Test
For this test, a chemical called guaiac is used to detect blood in the stool. A doctor may obtain a stool sample for this test during a rectal examination by using a gloved finger. This sample is placed on a piece of filter paper infused with guaiac. A second liquid chemical (peroxidase) is added, and the sample changes color if blood is present. More preferably, the person can take home a kit containing the filter papers. The person places samples of stool from about three different bowel movements on the filter papers, which are then mailed back to the doctor for testing. If blood is detected, further tests are needed to determine the source. Before doing this test, people may be told to avoid certain foods (such as red meat and cruciferous vegetables) and to limit their intake of vitamin C to less than 250 milligrams per day for 3 days before and during testing. 